#include <queue>
#include <iostream>
#include <vector>

struct Station {
    Station():marked(false){}
    bool marked;
    std::vector<int> children;
};
std::vector<Station> stations;
std::vector<bool> isSource;
std::vector<bool> isCollector;
int source = 0, collector = 0;

int nMarked = 0;
unsigned N, M;

bool count_pipes(const int st, const unsigned nodes) {
    if (stations[st].marked)
        return false;
    if (st == collector)
        return nodes == N;
    for (auto child : stations[st].children)
        if (count_pipes(child, nodes + 1))
            return true;
    return false;
}

int main() {
    std::cin >> N >> M;
    for (unsigned i = 0; i < N; i++)
        stations.push_back(Station());
    for (unsigned i = 0; i < N; i++) {
        isSource.push_back(true);
        isCollector.push_back(true);
    }
    
    for (unsigned i = 0; i < M; i++) {
        int s, t;
        std::cin >> s >> t;
        s--;
        t--;
        stations[s].children.push_back(t);
        isSource[t] = false;
        while (!isSource[source]) 
            source++;
        isCollector[s] = false;
        while(!isCollector[collector])
            collector++;
    }
    std::cout << (count_pipes(source, 1) ? M - (N - 1) : 0) << std::endl;
    return 0;
}

/*
5 6
2 4
3 5
2 5
1 4
2 3
5 1
*/

/*
4 4
1 2
1 3
2 4
3 4
*/

/*
5 5
1 2
1 3
2 4
3 4
4 5
*/