#include <bits/stdc++.h>
using namespace std;
const long long INF = 10e16;
const int maxN = 200010;
const int maxD = 15;
const int maxH = 100;
const int MOD = 1000000007;
long long x, y, z;
int main() {
  cin >> x;
  cin >> y;
  if (x == 1) {
    z = 1;
    cout << z << endl;
    return 0;
  }
  if (x % 2 == 0) {
    z = x * y / 2;
  } else {
    z = (x / 2) * y;
    z += (y % 2 == 0) ? y / 2 : y / 2 + 1;
  }
  cout << z << endl;
  return 0;
}
