C. 討論室 (discussion)

#include <bits/stdc++.h>
using namespace std;

int main() {
    ios_base::sync_with_stdio(0), cin.tie(0);

    int n, k; cin >> n >> k;

    vector<pair<int, int>> show(n);
    for (auto &[r, l] : show) cin >> l >> r;
    sort(begin(show), end(show));

    int ans = 0;
    multiset<int> st;
    for (int i = 0; i < k; ++i) st.emplace(0);
    for (auto [r, l] : show) {
        auto it = st.upper_bound(l);
        if (it != st.begin()) st.erase(prev(it)), st.emplace(r), ++ans;
    }
    cout << ans << "\n";

    return 0;
}