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#include <bits/stdc++.h>
using namespace std;
const int N = 100010, M = N << 1;
int n, m;
int h[N], e[M], ne[M], idx;
void add(int a, int b) {
e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}
int d[N];
int bfs() {
queue<int> q;
q.push(1);
d[1] = 0;
while (q.size()) {
auto u = q.front();
q.pop();
for (int i = h[u]; ~i; i = ne[i]) {
int j = e[i];
if (d[j] == -1) {
d[j] = d[u] + 1;
q.push(j);
}
}
}
return d[n];
}
int main() {
memset(h, -1, sizeof h);
memset(d, -1, sizeof d);
cin >> n >> m;
for (int i = 1; i <= m; i++) {
int a, b;
cin >> a >> b;
add(a, b);
}
cout << bfs() << endl;
return 0;
}