#include <iostream>
#include <cstring>

using namespace std;

const int N = 1e5 + 10;

int n, m;
int h[N], e[N], ne[N], idx;

int q[N]; //广度优先搜索队列
int d[N]; //各节点距离根节点的距离

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

int bfs()
{
    int tt = 0, hh = 0;
    memset(d, -1, sizeof d);
    q[0] = 1; //从1号节点开始遍历
    d[1] = 0; //1号节点到根节点的距离为0

    while(hh <= tt)
    {
        int t = q[hh ++ ];

        for(int i = h[t]; i != -1; i = ne[i])
        {
            int j = e[i];
            if(d[j] == -1)
            { 
                d[j] = d[t] + 1;
                q[++ tt] = j;
            }
        }
    }

    return d[n];
}

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

    memset(h, -1, sizeof h);

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

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