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