#include <iostream>
#include <cstring>
#include <algorithm>
#include <queue>

using namespace std;

const int N = 100010;

int h[N], e[N * 2], ne[N * 2], idx;
int dist[N];
bool st[N];
int n, m;

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

void bfs() {
    memset(dist, 0x3f, sizeof(dist));
    dist[1] = 0;
    st[1] = true;
    queue<int> q;
    q.push(1);

    while (q.size()) {
        int t = q.front();
        q.pop();
        for (int i = h[t]; i != -1; i = ne[i]) {
            int j = e[i];
            if (!st[j]) {
                dist[j] = dist[t] + 1;
                q.push(j);
                st[j] = true;
            }
        }
    }
}

int main(void)
{
    memset(h, -1, sizeof(h));

    cin >> n >> m;

    while (m--) {
        int a, b;
        cin >> a >> b;
        add(a, b);
    }

    bfs();

    if (dist[n] == 0x3f3f3f3f)
        cout << -1 << endl;
    else 
        cout << dist[n] <<endl;

    return 0;
}