#include<iostream>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;

const int N = 1e5 + 10;
int h[N], ne[N], e[N], idx;
int n, m;
bool st[N];
int dis[N];
queue<int> q;

void add(int a, int b) {
    e[idx] = b;
    ne[idx] = h[a];
    h[a] = idx ++ ;
}

int main() {
    memset(h, -1, sizeof h);
    memset(dis, 0x3f3f3f, sizeof dis);
    cin >> n >> m;
    for (int i = 0; i < m; i ++ ) {
        int a, b;
        cin >> a >> b;
        add(a, b);
    }
    dis[1] = 0;
    st[1] = true;
    q.push(1);
    while(!q.empty()) {
        int t = q.front();
        q.pop();
        for (int i = h[t]; i != -1; i = ne[i]) {
            int j = e[i];
            if (st[j]) continue;
            st[j] = true;
            dis[j] = dis[t] + 1;
            q.push(j);
        }
    }

    if(dis[n] != 0x3f3f3f3f) cout << dis[n] << endl;
    else cout << -1 << endl;
    return 0;
}