【題解】Codeforces 1252H. Twin Buildings

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
 
int n;
long long l, w, mx, ans;
vector <pair<long long, long long> > v;
 
int main() {
    cin >> n;
    for (int i = 0; i < n; i++){
        cin >> l >> w;
        if (l < w) swap(l, w);
        v.push_back({l, w});
    }
    sort(v.rbegin(), v.rend());
    for (int i = 0; i < n; i++){
        ans = max(ans, v[i].first * min(mx, v[i].second) * 2);
        ans = max(ans, v[i].first * v[i].second);
        mx = max(mx, v[i].second);
    }
    cout << ans/2;
    if (ans % 2 == 0) cout << ".0\n";
    else cout << ".5\n";
}