#include <iostream> #include <string> #include <cstdio> #include <algorithm> #include <vector> using namespace std; int dp[100001]; int M, N; int main(void) { int x, y; cin >> N >> M; for (int i = 0; i < M; i++) { cin >> x >> y; if (dp[y] == 0) { dp[y] = dp[x] + 1; } else if( dp[y] > dp[x] + 1){ dp[y] = dp[x] + 1; } } cout << dp[N] << endl; return 0; }