#include <iostream>
#include <string.h>
#include <queue>
#include <vector>
#include <utility>
#define Nsize 100001
using namespace std;
int N, M; // N : 노드의 갯수, 선 갯수
vector<int> arr[Nsize];
int dist[Nsize];
int BFS(int cur) {
queue<pair<int,int> > que;
que.push(make_pair(1,0));
while (!que.empty()) {
int out = que.front().first;
int out_dist = que.front().second + 1;
que.pop();
for (int i = 0 ; i < arr[out].size(); i++) {
if (arr[out][i] == N) {
return out_dist;
}
if (dist[arr[out][i]] == -1) {
dist[arr[out][i]] = out_dist;
que.push(make_pair(arr[out][i], out_dist));
}
}
}
return -1;
}
int main() {
memset(dist, -1, sizeof(dist));
cin >> N >> M;
int temp1, temp2;
for (int i = 0 ; i < M; i++) {
cin >> temp1 >> temp2;
arr[temp1].push_back(temp2);
}
cout << BFS(1) << endl;
return 0;
}
