#include <iostream>
#include <cstring>
#include <queue>
using namespace std;
const int N = 1E5 + 10;
int head[N], value[N*2], nxt[N*2];
int idx;
int n, m;
void add(int a, int b){
    value[idx] = b;
    nxt[idx] = head[a];
    head[a] = idx ++ ;
}
void read(){
    memset(head, -1, sizeof head);
    cin >> n >> m;
    int a, b;
    while(m -- ){
        scanf("%d%d", &a, &b);
        add(a, b);
    }
}
int dist[N];
int bfs(){
    memset(dist, -1, sizeof dist);
    queue<int> qu;
    qu.push(1); 
    dist[1] = 0;
    while(!qu.empty()){
        int now = qu.front();
        qu.pop();
        for(int i = head[now]; i != -1; i = nxt[i]){
            int p = value[i];
            if(dist[p] == -1){
                dist[p] = dist[now] + 1;
                qu.push(p);
            }
        }
    }
    return dist[n];
}
int main(){
    read();
    cout << bfs() << endl;
    return 0;
}