#include <cstdio>

#include <cstring>

#include <iostream>

#include <algorithm>

#include <queue>

using namespace std;

const int N = ;

int n, m;

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

int d[N];

void add(int a, int b) {

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

}

int bfs() {

    memset(d, -, sizeof d);

    queue<int> q;

    d[] = ;

    q.push();

    while (q.size()) {//当队列不空

        int t = q.front();//取得队头

        q.pop();

        for (int i = h[t]; i != -; i = ne[i]) {

            int j = e[i];//j扩展

            if (d[j] == -) {//如果没有被遍历过

                d[j] = d[t] + ;//扩展

                q.push(j);//插入

            }

        }

    }

    return d[n];

}

int main() {

    scanf("%d%d", &n, &m);

    memset(h, -, sizeof h);

    for (int i = ; i < m; i ++ ) {

        int a, b;

        scanf("%d%d", &a, &b);

        add(a, b);

    }

    cout << bfs() << endl;

    return ;

}

#include<bits/stdc++.h>

using namespace std ;

const int N=;

int n,m;

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

int d[N],q[N];

void add(int a,int b)

{

    e[idx]=b;

    ne[idx]=h[a];

    h[a]=idx++;

}

int bfs()

{

    int hh=,tt=;

    q[]=;

    memset(d,-,sizeof d);

    d[]=;

    while(hh<=tt)//当队列不空

    {

        int t=q[hh++];//取队头

        for(int i=h[t];i!=-;i=ne[i])//扩展

        {

            int j=e[i];

            if(d[j]==-)

            {

                d[j]=d[t]+;

                q[++tt]=j;

            }

        }

    }

    return d[n];

}

int main()

{

    cin>>n>>m;

    memset(h,-,sizeof h);

    for(int i=;i<m;i++)

    {

        int a,b;

        cin>>a>>b;

        add(a,b);

    }

    cout<<bfs()<<endl;

}