#include<iostream>
#include<cstdio>
using namespace std;
#define re register
#define Re register
#define MAXN 300005
#define ll long long
int n,S,hh,tt,q[MAXN];
ll opt[MAXN];
struct task{
    ll t,c;
}a[MAXN],s[MAXN];
int main() {
    scanf("%d%d",&n,&S);
    q[0] = 0;
    for(re int i = 1;i <= n;i++){
        scanf("%d%d",&a[i].t,&a[i].c);
        s[i].t = s[i - 1].t + a[i].t;
        s[i].c = s[i - 1].c + a[i].c;
    }
    for(re int i = 1;i <= n;i++){
        while(hh < tt && opt[q[hh + 1]] - opt[q[hh]] <= (s[i].t + S) * (s[q[hh + 1]].c - s[q[hh]].c))hh++;
        int j = q[hh];
        opt[i] = opt[j] - (s[i].t + S) * s[j].c + s[i].t * s[i].c + S * s[n].c;
        while(hh < tt && (opt[q[tt]] - opt[q[tt - 1]]) * (s[i].c - s[q[tt - 1]].c) >= (opt[i] - opt[q[tt - 1]]) * (s[q[tt]].c - s[q[tt - 1]].c))tt--;
        q[++tt] = i;
    }
    cout << opt[n] << endl;
    return 0;
}