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

class unionfind {
    vector<int> par;

public:
    unionfind(int n) {
        for (int i = 0; i < n; i++) {
            par.push_back(i);
        }
    }

    int find(int n) {
        if (par.at(n) == n) return n;
        return par.at(n) = find(par.at(n));
    }

    void merge(int m, int n) {
        m = find(m);
        n = find(n);
        if (m == n) return;
        par.at(m) = n;
    }
};

int main() {
    int n, m;
    cin >> n >> m;
    vector<int> b(n), c(n);
    for (int i = 0; i < n; i++) {
        cin >> b.at(i) >> c.at(i);
        b.at(i)--;
        c.at(i)--;
    }
    vector<vector<int>> color(n);
    for (int i = 0; i < n; i++) {
        color.at(c.at(i)).push_back(b.at(i));
    }
    unionfind t(m);
    for (int i = 0; i < n; i++) {
        for (int v : color.at(i)) {
            t.merge(v, color.at(i).at(0));
        }
    }
    set<int> s;
    for (int i = 0; i < m; i++) {
        s.insert(t.find(i));
    }
    cout << m - s.size() << endl;
}