#include <bits/stdc++.h>
using namespace std;
int main() {
  long long H, W;
  cin >> H >> W;
  long long first_row, second_row;
  long long sum;
  if (W % 2 == 0) {
    first_row = W / 2;
    second_row = first_row;
  } else {
    first_row = (W + 1) / 2;
    second_row = first_row - 1;
  }
  if (H % 2 == 0) {
    sum = (first_row + second_row) * (H / 2);
  } else {
    sum = (first_row + second_row) * ((H + 1) / 2) - second_row;
  }
  cout << sum << endl;
}
