#include <bits/stdc++.h>
using namespace std;
int main() {
  int H, W, x, y;
  double z;
  cin >> H >> W;
  x = H * W;
  y = x % 2;
  z = x / 2;
  if (H == 1 && W > 1)
    cout << 1;
  else if (H == 1 && W < 1)
    cout << 1;
  else if (W == 1 && H > 1)
    cout << 1;
  else if (W == 1 && H < 1)
    cout << 1;
  else if (W == 1 && H == 1)
    cout << 0;
  else if (y == 0)
    cout << z;
  else
    cout << z + 0.5;
}
