#include <bits/stdc++.h>
int main(void) {
  int H, W, X;
  long Y;
  scanf("%d  %d", &H, &W);
  if (H == 1 || W == 1) {
    printf("1");
  }
  if (H * W % 2 == 0) {
    X = (H * W) / 2;
    printf("%d", X);
  } else {
    Y = (H * W) / 2 + 1;
    printf("%1d", Y);
  }
  return 0;
}
