#include<iostream>
#include<algorithm>
#include<vector>
#include<cstdio>
#include<queue>
#include<deque>
using namespace std;
const int MAX_V = 200005;
const int INF = 987654321;
int V;
vector<pair<int, int> > adj[MAX_V];
vector<int> dijkstra(int src) {
vector<int> dist(V, INF);
dist[src] = 0;
priority_queue<pair<int, int> > pq;
pq.push(make_pair(0, src));
while(!pq.empty()) {
int cost = -pq.top().first;
int here = pq.top().second;
pq.pop();
if(dist[here] < cost) continue;
for(int i = 0; i < adj[here].size(); ++i) {
int there = adj[here][i].first;
int nextDist = cost + adj[here][i].second;
if(dist[there] > nextDist) {
dist[there] = nextDist;
pq.push(make_pair(-nextDist, there));
}
}
}
if(dist[V - 1] == INF) printf("-1");
else printf("%d", dist[V - 1]);
return dist;
}
int main()
{
int n, m;
scanf("%d %d", &n, &m);
V = n + 1;
for(int i = 0; i < m; i++) {
int a, b;
scanf("%d %d", &a, &b);
adj[a].push_back(make_pair(b, 1));
}
dijkstra(1);
}
