#include <bits/stdc++.h>   using namespace std;   int main() {     int m, n;     cin >> m >> n;     cout << ((m % 2) ? m * (n / 2) + (n % 2) * (m / 2)                      : n * (m / 2) + (m % 2) * (n / 2));     return 0;   }   