#include<iostream>
#include<cstring>
using namespace std;
const int N = 1e5 + 5;
int e[N], ne[N], h[N], id;
int d[N] , q[N]; bool st[N];
void add(int a, int b){
    e[id] = b;
    ne[id] = h[a];
    h[a] = id++;
}
int n;
int bfs(int u){
    st[u] = true;
    int tt = 0, hh  = 0;
    d[1] = 0;
    while(hh <= tt){
        int j = q[hh++];
        for(int i = h[j]; i != -1; i = ne[i]) {
            int r = e[i];
            if(!st[r]){
                d[r] = d[j] + 1;
                q[++tt] = r;
                st[r] = true;
            }
        }
    }
    return d[n];
}

int main(){
    memset(h, -1, sizeof h);
    int n, m;
    cin >> n >> m;
    for(int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        add(a, b);

    }
    q[0] = 1;
    bfs(1);
    if(d[n] == 0) cout<<-1;
    else cout<<d[n];
    return 0;

}