#include<bits/stdc++.h>
#define deb(var) cerr<<"deb: "<< #var <<'='<<(var)<<'\n'
#define mids(l,r) const auto mid = l + r >> 1
#define cint const int&
#define ll long long
#define inf 0x3f3f3f3f3f3f3f3f3f
#define ls (x<<1)
#define rs (ls|1)
#define lb(x) x&-x
using namespace std;
const int maxn = 1e5+10;
int ans = inf;
struct{
    int nxt,v;
}edge[maxn << 1];
int head[maxn],cnt;
inline void addedge(cint a,cint b){
    edge[++cnt] = {head[a],b};
    head[a] = cnt;
}
int u,v,n,m;
int dis[maxn],q[maxn],hd,tl = 1;
inline void bfs(cint s){
    dis[q[++hd] = s] = 1;

    while(hd <= tl){
        const int u = q[hd++];
        for(int i = head[u];i;i=edge[i].nxt ){
            const int v = edge[i].v;
            if(dis[v])  continue;
            dis[q[++tl] = v] = dis[u] + 1;
        }
    }
}
signed main() {
    ios::sync_with_stdio(0),cin.tie(0);
//  ifstream ifs(".in");
//  ofstream ofs(".out");
//  cin.rdbuf(ifs.rdbuf()),cout.rdbuf(ofs.rdbuf());
    cin>>n>>m;
    for(int i = 1;i<=m;++i){
        cin>>u>>v;
        addedge(u,v);
    }
    bfs(1);
    cout<<(dis[n]?dis[n]-1:-1);
}