#include <iostream>
#include <set>
#include <vector>

using namespace std;

int main(){
    while (1){
        int n, m;
        cin >> n >> m;
        if (n == 0 && m == 0) break;

        vector<vector<int> > mat = vector<vector<int> >(n);
        vector<set<int> > inDegree = vector<set<int> >(n + 1);

        vector<int> auxInDegree = vector<int>(n, 0);
        while (m--){
            int d, u;
            cin >> d >> u;
            mat[d-1].push_back(u-1);
            auxInDegree[u-1]++;
        }

        for (int i = 0; i < n; i++){
            inDegree[ auxInDegree[i] ].insert(i);
        }

        int ans = 1;
        for (int i = 0; i < n; i++){
            int sz0 = inDegree[0].size();
            if (sz0 == 0){
                ans = 0;
                break;
            }
            if (sz0 > 1){
                ans = 2;
            }
            int x = *(inDegree[0].begin());inDegree[0].erase(x);
            for (vector<int>::iterator it = mat[x].begin(); it != mat[x].end(); it++){
                int y = *it;
                inDegree[ auxInDegree[y] ].erase(y);
                auxInDegree[y]--;
                inDegree[ auxInDegree[y] ].insert(y);
            }
        }

        cout << ans << endl;
    }
    return 0;
}