#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll = long long;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;
using VD = vector<double>;
using VVD = vector<VD>;
using VS = vector<string>;
using P = pair<ll,ll>;
using VP = vector<P>;
#define rep(i, n) for (ll i = 0; i < ll(n); i++)
#define out(x) cout << x << endl
#define dout(x) cout << fixed << setprecision(10) << x << endl
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define sz(x) (int)(x.size())
#define re0 return 0
#define pcnt __builtin_popcountll
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
constexpr int inf = 1e9;
constexpr ll INF = 1e18;
//using mint = modint1000000007;
using mint = modint998244353;
int di[4] = {1,0,-1,0};
int dj[4] = {0,1,0,-1};

int main(){
    ll n,m;
    cin >> n >> m;
    VVL col(n); //col[i]:色iを持つスライムが入っている箱のリスト
    rep(i,n){
        ll b,c;
        cin >> b >> c;
        b--,c--;
        col[c].emplace_back(b);
    }
    dsu uf(m);
    ll ans = 0;
    rep(i,n){
        rep(j,sz(col[i])-1){
            if(!uf.same(col[i][j],col[i][j+1])){
                ans++;
                uf.merge(col[i][j],col[i][j+1]);
            }
        }
    }
    out(ans);
}