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

using namespace std;

const int N = 100010;

int n, m;
int h[N], e[N], ne[N], idx;
int d[N];
queue<int> q;

// 添加一条a指向b的边
void add(int a, int b) {
    e[idx] = b;
    ne[idx] = h[a];
    h[a] = idx++;
}

// 1号点到n号点的最短距离，不存在就返回-1
int bfs() {;
    q.push(1);
    d[1] = 0;

    while(q.size()) {
        int t = q.front();
        q.pop();

        // 遍历邻接表中所有下一层结点
        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()
{
    cin >> n >> m;

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

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

        add(a, b);
    }

    cout << bfs() << endl;
    return 0;
}