#include <bits/stdc++.h>
int main() {
  long long i;
  long long j;
  long long range;
  long long result;
  scanf("%lld%lld", &i, &j);
  range = i * j;
  if (i == 1 || j == 1)
    result = 1;
  else if (range % 2 == 0)
    result = range / 2;
  else
    result = (range / 2) + 1;
  printf("%lld\n", result);
  return 0;
}
