#include <bits/stdc++.h>
int main() {
  unsigned int H, W, c = 0, i, j;
  std::cin >> H >> W;
  for (i = 1; i <= H; i++)
    for (j = 1; j <= W; j++)
      if ((i + j) % 2 == 0) c++;
  std::cout << c;
}
