text: #include <bits/stdc++.h>
  
  using namespace std;
  
  int main(){
      int n, m, resp = 0;
  
      cin >> n >> m;
  
      if(n >= 2 && m >= 2){
          resp += (n / 2) * (m / 2);
      }
      int a = (n % 2) * m;
      int b = (m % 2) * n;
  
      if(a % 2 == 1 || b % 2 == 1){
          resp++;
      }
  
      resp += a / 2;
      resp += b / 2;
  
      cout << resp << endl;
  
      return 0;
  }
  