#include<bits/stdc++.h>
using namespace std;

const int N = 100005;
int n, e[N], ne[N], h[N], idx = 1;
int d[N];
bool vis[N];
queue<int> q;

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

int bfs () {
    memset(d, -1, sizeof(d));
    q.push(1);
    d[1] = 0;
    while (!q.empty()) {
        int t = q.front(); q.pop();
        for (int i = h[t]; i != -1; i = ne[i]) {
            int j = e[i];
            if (d[j] == -1) {
                d[j] = d[t] + 1;
                q.push(j);
            }
        }
    }

    return d[n];
}

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

    return 0;
}