#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

class union_find {
  public:
    union_find(int n) : data(n, -1) {}
    int unite(int x, int y) {
        x = root(x), y = root(y);
        if(x != y) {
            if(size(x) < size(y)) swap(x, y);
            data[x] += data[y];
            return data[y] = x;
        }
        return -1;
    }
    int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }
    int size(int x) { return -data[root(x)]; }
    bool same(int x, int y) { return root(x) == root(y); }

  private:
    vector<int> data;
};

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    int N,M; cin >> N >> M;
    union_find uf(N);
    vector<pair<int,int>> bc(N);
    vector<int> box(M, -1);
    for(auto &[b, c] : bc) {
        cin >> b >> c; b--; c--;
        if(box[b] != -1) uf.unite(box[b], c);
        box[b] = c;
    }

    vector<set<int>> pos(N);
    for(auto &[b, c] : bc) {
        c = uf.root(c);
        pos[c].insert(b);
    }

    int ans = 0;
    for(auto st : pos) ans += max(0, int(st.size()) - 1);
    cout << ans << endl;
}