#include <bits/stdc++.h>
using namespace std;
bool chmin(long long int& a, long long int b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
bool chmax(long long int& a, long long int b) {
  if (b > a) {
    a = b;
    return 1;
  }
  return 0;
}
const long long int INF = 999999999999999;
const long long int MOD = 1000000007;
const long long int MAX_N = 500010;
long long int a, b, c, d, e, f, p, t, x, y, z, q, m, n, r, h, k, w, l, ans;
int main() {
  cin >> x >> y;
  if (x > 1 && y > 1) {
    cout << (x * y + 1) / 2 << endl;
  } else {
    cout << 1 << endl;
  }
}
