#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <class T> using vec = vector<T>;
template <class T> using vvec = vector<vec<T>>;
template<class T> bool chmin(T& a,T b){if(a>b) {a = b; return true;} return false;}
template<class T> bool chmax(T& a,T b){if(a<b) {a = b; return true;} return false;}
#define rep(i,n) for(int i=0;i<(n);i++)
#define drep(i,n) for(int i=(n)-1;i>=0;i--)
#define all(x) (x).begin(),(x).end()
#define debug(x)  cerr << #x << " = " << (x) << endl;

class UnionFind{
private:
    vec<int> p,s;
    int cnt;
public:
    UnionFind(){}
    UnionFind(int N):cnt(N),s(N,1),p(N){
        iota(p.begin(),p.end(),0);
    }
    int find(int x){
        if(p[x]==x) return x;
        else return p[x] = find(p[x]);
    }
    void unite(int x,int y){
        x = find(x); y = find(y);
        if(x==y) return;
        if(s[x]>s[y]) swap(x,y);
        p[x] = y;
        s[y] += s[x];
        cnt--;
    }
    int operator[](const int x){return find(x);}
    bool is_same_set(int x,int y) {return find(x)==find(y);}
    int size(int x) {return s[find(x)];}
    int compnents_number(){return cnt;}
};

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N,M;
    cin >> N >> M;
    vvec<int> C(N);
    rep(i,N){
        int b,c;
        cin >> b >> c;
        b--,c--;
        C[c].push_back(b);
    }
    UnionFind uf(M);
    for(auto& v:C){
        for(auto& x:v){
            uf.unite(v[0],x);
        }
    }
    cout << M-uf.compnents_number() << "\n";
}