#include <bits/stdc++.h>
#define For(i, a, b) for (int(i) = (int)(a); (i) < (int)(b); ++(i))
#define rFor(i, a, b) for (int(i) = (int)(a)-1; (i) >= (int)(b); --(i))
#define rep(i, n) For((i), 0, (n))
#define rrep(i, n) rFor((i), (n), 0)
#define fi first
#define se second
using namespace std;
typedef long long lint;
typedef unsigned long long ulint;
typedef pair<int, int> pii;
typedef pair<lint, lint> pll;
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 (a > b) {
        a = b;
        return true;
    }
    return false;
}
template <class T>
T div_floor(T a, T b) {
    if (b < 0) a *= -1, b *= -1;
    return a >= 0 ? a / b : (a + 1) / b - 1;
}
template <class T>
T div_ceil(T a, T b) {
    if (b < 0) a *= -1, b *= -1;
    return a > 0 ? (a - 1) / b + 1 : a / b;
}

constexpr lint mod = 1000000007;
constexpr lint INF = mod * mod;
constexpr int MAX = 200010;

typedef struct UnionFindTree {
    vector<int> par;

    UnionFindTree(int n) { par.resize(n, -1); }

    bool is_root(int x) { return par[x] < 0; }

    int find(int x) {
        if (is_root(x)) return x;
        return par[x] = find(par[x]);
    }

    int size(int x) { return -par[find(x)]; }

    bool unite(int x, int y) {
        x = find(x);
        y = find(y);
        if (x == y) return false;
        if (size(x) < size(y)) swap(x, y);
        par[x] += par[y];
        par[y] = x;
        return true;
    }

    bool same(int x, int y) { return find(x) == find(y); }
} UF;

int main() {
    int n, m;
    scanf("%d%d", &n, &m);
    vector<int> box[m];
    UF uf(n);
    bool used[n];
    memset(used, false, sizeof(used));
    rep(i, n) {
        int b, c;
        scanf("%d%d", &b, &c);
        --b;
        --c;
        box[b].push_back(c);
        used[c] = true;
    }

    int ans = -n;
    ans += count_if(used, used + n, [](bool x) { return !x; });
    rep(i, m) {
        if (!box[i].empty()) {
            ++ans;
            rep(j, box[i].size() - 1) {
                ans += uf.unite(box[i][j], box[i][j + 1]);
            }
        }
    }
    printf("%d\n", ans);
}