//Основы теории графов и dfs. Теория. Задача G.
#include <bits/stdc++.h>
using namespace std;
int n, m;
vector < vector < int > > g;
vector < int > color;
vector < int > cur;
int is = 0;

void dfs(int v, int p) {
    if (color[v] == 1) {
        is = max(is, 1);
        return;
    }
    color[v] = 1;
    for (auto u : g[v]) {
        if (u != p) {
            dfs(u, v);
        }
    }
    color[v] = 2;
}

int main() {
    cin >> n >> m;
    g.resize(n);
    color.resize(n, 0);
    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        a--; b--;
        g[a].push_back(b);
    }
    for (int i = 0; i < n; i++) {
        if (color[i] == 0) {
            dfs(i, -1);
        }
    }
    cout << is;
    return 0;
}