#include<bits/stdc++.h>
using namespace std;

struct UnionFind {
    vector<int> par;
    vector<int> size;
    UnionFind(int n) {
        par.resize(n);
        size.resize(n,1);
        for(int i = 0; i < n; i++) {
            par[i] = i;
        }
    }
    int find(int x) {
        if(par[x] == x) {
            return x;
        }
        return par[x] = find(par[x]);
    }
    bool same(int x, int y) {
        return find(x) == find(y);
    }
    int consize(int x) {
        return size[find(x)];
    }
    bool unite(int x, int y) {
        x = find(x);
        y = find(y);
        if(x == y) {
            return false;
        }
        if(size[x] > size[y]) {
            swap(x,y);
        }
        par[x] = y;
        size[y] += size[x];
        return true;
    }
};

int main() {
    int N,M;
    cin >> N >> M;
    vector<int>cnt(N);
    vector<vector<int>>road(N);
    UnionFind uf(N);
    for(int i = 0; i < M; i++) {
        int A,B;
        cin >> A >> B;
        A--;
        B--;
        uf.unite(A,B);
        road[A].push_back(B);
        cnt[B]++;
    }
    map<int,pair<int,int>>tmp;
    for(int i = 0; i < N; i++) {
        if(!cnt[i]) {
            tmp[uf.find(i)].first++;
        }
        if(road[i].empty()) {
            tmp[uf.find(i)].second++;
        }
    }
    int ans = 0,ret = 0;
    for(auto i:tmp) {
        ans += max(i.second.second,i.second.first);
        if(i.second.second > 0 || i.second.first > 0) {
            ret++;
        }
    }
    cout << min(N,ans-max(0,ret-1)+(int)tmp.size()-1+min(1,ret)) << endl;
}