#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < int(n); i++)
#define rrep(i,n) for(int i = int(n)-1; i >= 0; i--)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define pb push_back
using namespace std;
using ll = long long;
using Pi = pair<int,int>;
using Pll = pair<ll,ll>;
template<class T> bool chmax(T &a, const T &b) {if(a < b) {a = b; return true;} return false;}
template<class T> bool chmin(T &a, const T &b) {if(b < a) {a = b; return true;} return false;}
int dx[] = {1, 0,-1, 0, 1, 1,-1,-1};
int dy[] = {0, 1, 0,-1, 1,-1, 1,-1};
ll mod = 998244353;
ll MOD = 1000000007;
int inf = 1001001001;
ll INF = 1001001001001001001;
struct UnionFind {
    vector<int>par;
    vector<int>size;
    UnionFind(int x) {
        par.resize(x);
        size.resize(x, 1);
        for(int i = 0; i < x; 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)];
    }
    void unite(int x, int y) {
        x = find(x);
        y = find(y);
        if(x == y) {
            return;
        }
        if(size[x] < size[y]) {
            par[x] = y;
            size[y] += size[x];
        }
        else {
            par[y] = x;
            size[x] += size[y];
        }
    }
};
int main() {
    int N,M;
    cin >> N >> M;
    vector<int>b(N),c(N);
    UnionFind uf(N);
    map<int,set<int>>tmp;
    rep(i,N) {
        cin >> b[i] >> c[i];
        b[i]--;c[i]--;
        tmp[b[i]].insert(c[i]);
    }
    for(pair<int,set<int>>x:tmp) {
        int c = *x.second.begin();
        for(int y:x.second) {
            uf.unite(c,y);
        }
    }
    map<int,set<int>>tmp2;
    rep(i,N) {
        tmp2[uf.find(c[i])].insert(b[i]);
    }
    int ans = 0;
    for(pair<int,set<int>> x:tmp2) {
        ans += x.second.size()-1;
    }
    cout << ans << endl;
}