#include <bits/stdc++.h>

using namespace std;

const int N = 1E5 + 10;

int h[N], e[N], ne[N], idx;
int d[N];
int st[N];
int n, m;
typedef pair<int, int> PII;
priority_queue<PII, vector<PII>, greater<PII>> q;

int main()
{
    cin >> n >> m;

    memset(h, -1, sizeof h);
    memset(d, 0x3f, sizeof d);

    for(int i = 0; i < m; i ++)
    {
        int a, b;
        cin >> a >> b;

        e[idx] = b;
        ne[idx] = h[a];
        h[a] = idx ++;
    }

    q.push({0, 1});
    st[1] = 1;
    d[1] = 0;

    while(q.size())
    {
        auto t = q.top();
        q.pop();

        int a = t.first, b = t.second;

        st[b] = 0;

        for(int i = h[b]; i != -1; i = ne[i])
        {
            int j = e[i];

            if(!st[j] and d[j] > a + 1)
            {
                d[j] = a + 1;
                q.push({d[j], j});
                st[j] = 1;
            }
        }
    }

    if(d[n] == 0x3f3f3f3f)
        cout << -1;

    else
        cout << d[n];
}