#include<iostream>
#include<cmath>
#include<algorithm>

using namespace std;
const int N=1010;
struct Point{
    double l,r;
}point[N];
bool cmp(Point a,Point b){
    return a.r<b.r;
}
int n,d;
int main(){
    scanf("%d%d",&n,&d);

    for(int i=1;i<=n;i++){
        int x,y;
        scanf("%d%d",&x,&y);
        if(abs(y)>d) {
            puts("-1");
            return 0;
        }
        double distance=sqrt(d*d-y*y);
        point[i]={x-distance,x+distance};

    }

    sort(point+1,point+1+n,cmp);
    double res=0,ed=-1e20;
    for(int i=1;i<=n;i++){
        if(point[i].l>ed){
            res++;
            ed=point[i].r;
        }
    }

    cout<<res<<endl;

    return 0;
}

#include<iostream>
#include<algorithm>
#include<queue>

using namespace std;
typedef pair<int,int> PII;
const int N=50010;

struct Range{
    int l,r,idx;
}range[N];
bool cmp(Range a,Range b){
    return a.l<b.l;
}
int ids[N];
int n;
int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++) {
        int start,end;
        scanf("%d%d",&start,&end);
        range[i]={start,end,i};
    }

    sort(range+1,range+1+n,cmp);
    int id=1;
    priority_queue<PII,vector<PII>,greater<PII>> heap;
    for(int i=1;i<=n;i++){
        auto point=range[i];
        if(heap.empty()||heap.top().first>=point.l){
            heap.push({point.r,point.idx});
            ids[point.idx]=id;
            id++;
        } 
        else{
            auto t=heap.top();
            heap.pop();
            ids[point.idx]=ids[t.second];
            heap.push({point.r,point.idx});
        }


    }
    cout<<heap.size()<<endl;
    for(int i=1;i<=n;i++) cout<<ids[i]<<endl;
    return 0;    
}

#include <iostream>
#include<algorithm>
using namespace std;
const int N=3500;
int n,m,i,j,k;
struct node
{
    int spf,cover;
} a[N];
struct node2
{
    int min_spf,max_spf;
} b[N];

int cmp(node a,node b)
{
    if (a.spf==b.spf)
        return a.cover>b.cover;
    return a.spf>b.spf;
}
int cmp2(node2 a,node2 b)
{
    if (a.min_spf==b.min_spf)
        return a.max_spf>b.max_spf;
    return a.min_spf>b.min_spf;
}
int main()
{
    cin>>n>>m;
    for (i=1;i<=n;i++)
        cin>>b[i].min_spf>>b[i].max_spf;
    sort(b+1,b+1+n,cmp2);
    for (i=1;i<=m;i++)
        cin>>a[i].spf>>a[i].cover;
    sort(a+1,a+1+m,cmp);
    int ans=0;
    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            if(a[j].cover>=1&&b[i].min_spf<=a[j].spf&&b[i].max_spf>=a[j].spf){
                a[j].cover--;
                ans++;
                break;
            }
        }
    }

    cout<<ans<<endl;
    return 0;    
}

#include<iostream>

using namespace std;
const int N=1e5+10;
int price[N];
int n;
int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++) scanf("%d",&price[i]);
    int res=0;
    for(int i=1;i<n;i++){
        if(price[i]<price[i+1]){
            res+=price[i+1]-price[i];
        }
    }

    cout<<res<<endl;
    return 0;
}

#include<iostream>

using namespace std;
typedef long long LL;
int n,m;
int gcd(int a,int b){
    return b?gcd(b,a%b):a;
}
LL C(int a){
    return (LL)(a)*(a-1)*(a-2)/6; 
}

int main(){
    cin>>n>>m;
    n++,m++;
    LL res = C(n * m) - (LL)n * C(m) - (LL)m * C(n);

    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            res-=2ll*((n-i)*(m-j))*(gcd(i, j) - 1);

        }
    }
    cout<<res<<endl;
    return 0;
}

#include<iostream>
using namespace std;
const int N = 100010, mod = 5000011;
int f[N],s[N];
int main(){
    int n,k;
    cin>>n>>k;

    f[0]=s[0]=1;
    for(int i=1;i<=n;i++){
        f[i]+=s[max(0,i-k-1)];
        s[i]=(s[i-1]+f[i])%mod;
    }
    cout<<s[n];


    return 0;
}

#include <iostream>
#include <cmath>

using namespace std;

int w[25],c[25];
const int MOD=1e9;
const int N=1e6;
int n;
int f[N+10];
void qui(long long a,int b){
    int cnt=1;
    int res=1;
    while(b){
        w[cnt++]=res;
        b--;
        res=(res*a);
    }
}

int main(){
    scanf("%d",&n);
    cin>>n;
    qui(2,21);


    f[0]=1;
    for(int i=1;i<=21;i++){
        for(int j=w[i];j<=n;j++){
            f[j]=(f[j]+f[j-w[i]])%MOD;
        }
    }
    cout<<f[n];
    return 0;
}

#include<iostream>

using namespace std;
const int N=2020;
long long f[N][N];
const int MOD=998244353;
int main(){
    int n,m,k;
    scanf("%d%d%d",&n,&m,&k);



    for(int i=1;i<=n;i++) f[i][0]=m;

    for(int i=2;i<=n;i++){
        for(int j=1;j<=k;j++){
            f[i][j]=(f[i-1][j-1]*(m-1)+f[i-1][j])%MOD;
        }
    }

    cout<<f[n][k];
    return 0;
}

#include <iostream>
#include <algorithm>

using namespace std;

typedef long long LL;

const int N = 100010, mod = 1e9 + 7;


int fact[N], infact[N];


int qmi(int a, int k, int p)
{
    int res = 1;
    while (k)
    {
        if (k & 1) res = (LL)res * a % p;
        a = (LL)a * a % p;
        k >>= 1;
    }
    return res;
}


int main()
{
    fact[0] = infact[0] = 1;
    for (int i = 1; i < N; i ++ )
    {
        fact[i] = (LL)fact[i - 1] * i % mod;
        infact[i] = (LL)infact[i - 1] * qmi(i, mod - 2, mod) % mod;
    }


    int n;
    scanf("%d", &n);
    while (n -- )
    {
        int a, b;
        scanf("%d%d", &a, &b);
        printf("%d\n", (LL)fact[a] * infact[b] % mod * infact[a - b] % mod);
    }

    return 0;
}

#include<iostream>

using namespace std;
const int MOD=1e9+7;
int c[2005][2005];
void init(){
    for(int i=0;i<=2001;i++){
        for(int j=0;j<=i;j++){
            if(!j) c[i][j]=1;
            else c[i][j]=(c[i-1][j]+c[i-1][j-1])%MOD;
        }
    }
}

int main(){

    init();
    int n;
    scanf("%d",&n);
    while(n--){
        int a,b;
        scanf("%d%d",&a,&b);
        printf("%d\n",c[a][b]);
    }


    return 0;
}