#include <iostream>
#include <vector>
#include <deque>
#include <numeric>

class UnionFind {
    std::vector<int> m_root;
    std::vector<int> m_depth;
    std::vector<int> m_size;
public:
    UnionFind(int size) :
        m_root(size),
        m_depth(size, 0),
        m_size(size, 1) {
        std::iota(m_root.begin(), m_root.end(), 0);
    }
    void unite(int x, int y) {
        x = root(x); y = root(y);
        if(x == y) { return; }
        auto t = size(x) + size(y);
        m_size[x] = m_size[y] = t;
        if(m_depth[x] < m_depth[y]) { m_root[x] = y; } else { m_root[y] = x; }
        if(m_depth[x] == m_depth[y]) { ++m_depth[x]; }
    }
    bool isSame(int x, int y) {
        return root(x) == root(y);
    }
    int root(int x) {
        if(m_root[x] == x) { return x; }
        return m_root[x] = root(m_root[x]);
    }
    int size(int x) {
        if(m_root[x] == x) { return m_size[x]; }
        return size(m_root[x] = root(m_root[x]));
    }
};

using ll = long long;
using std::cout;
using std::cin;
constexpr char endl = '\n';

signed main() {
    ll n, m;
    cin >> n >> m;
    std::vector<std::deque<ll>> cv(n);
    for(int _ = 0; _ < n; ++_) {
        ll b, c;
        cin >> b >> c;
        cv[c - 1].emplace_back(b - 1);
    }

    auto dsu = UnionFind(m);

    ll ans = 0;
    for(const auto& dq : cv) if(!dq.empty()) {
        auto base = dq.front();
        for(const auto& tg : dq) {
            if(!dsu.isSame(base, tg)) {
                dsu.unite(base, tg);
                ++ans;
            }
        }
    }
    cout << ans << endl;
}