#include <bits/stdc++.h>
#define rep(i, n) for(int(i) = 0; (i) < (n); (i)++)
#define FOR(i, m, n) for(int(i) = (m); (i) < (n); (i)++)
#define ALL(v) (v).begin(), (v).end()
#define LLA(v) (v).rbegin(), (v).rend()
#define SZ(v) (v).size()
#define INT(...)                                                               \
    int __VA_ARGS__;                                                           \
    read(__VA_ARGS__)
#define LL(...)                                                                \
    ll __VA_ARGS__;                                                            \
    read(__VA_ARGS__)
#define DOUBLE(...)                                                            \
    double __VA_ARGS__;                                                        \
    read(__VA_ARGS__)
#define CHAR(...)                                                              \
    char __VA_ARGS__;                                                          \
    read(__VA_ARGS__)
#define STRING(...)                                                            \
    string __VA_ARGS__;                                                        \
    read(__VA_ARGS__)
#define VEC(type, name, size)                                                  \
    vector<type> name(size);                                                   \
    read(name)
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using Graph = vector<vector<int>>;
template <typename T> struct edge {
    int to;
    T cost;
    edge(int t, T c) : to(t), cost(c) {}
};
template <typename T> using WGraph = vector<vector<edge<T>>>;
const int INF = 1 << 30;
const ll LINF = 1LL << 60;
const int MOD = 1e9 + 7;
template <class T> inline vector<T> make_vec(size_t a, T val) {
    return vector<T>(a, val);
}
template <class... Ts> inline auto make_vec(size_t a, Ts... ts) {
    return vector<decltype(make_vec(ts...))>(a, make_vec(ts...));
}

void read() {}
template <class T> inline void read(T &a) { cin >> a; }
template <class T, class S> inline void read(pair<T, S> &p) {
    read(p.first), read(p.second);
}
template <class T> inline void read(vector<T> &v) {
    for(auto &a : v)
        read(a);
}
template <class Head, class... Tail>
inline void read(Head &head, Tail &...tail) {
    read(head), read(tail...);
}
template <class T> inline void chmax(T &a, T b) { (a < b ? a = b : a); }
template <class T> inline void chmin(T &a, T b) { (a > b ? a = b : a); }

// UnionFind
struct UnionFind {
    vector<ll> par;
    vector<ll> siz;

    UnionFind(ll N) : par(N), siz(N, 1LL) {
        for(int i = 0; i < N; i++)
            par[i] = i;
    }
    int root(int x) {
        if(par[x] == x)
            return x;
        return par[x] = root(par[x]);
    }
    void unite(int x, int y) {
        int rx = root(x);
        int ry = root(y);
        if(rx == ry)
            return;
        if(siz[rx] < siz[ry])
            swap(rx, ry);
        siz[rx] += siz[ry];
        par[ry] = rx;
    }
    bool same(int x, int y) {
        int rx = root(x);
        int ry = root(y);
        return rx == ry;
    }
    ll size(ll x) { return siz[root(x)]; }
};

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    INT(n, m);
    vector<set<int>> sets(n);
    rep(i, n) {
        INT(b, c);
        b--, c--;
        sets[c].insert(b);
    }
    int res = 0;
    UnionFind uf(m);
    rep(i, n) {
        if(sets[i].size() >= 2) {
            auto it = sets[i].begin();
            for(auto num : sets[i])
                uf.unite(*it, num);
        }
    }

    rep(i, m) {
        if(uf.root(i) == i)
            res += uf.size(i) - 1;
    }
    cout << res << endl;
}