#include <bits/stdc++.h>

using namespace std;

int32_t main() { 
  cin.tie(0)->sync_with_stdio(0);

  int n, m; cin >> n >> m;

  int answer = 0;
  for (int i = 1, pass = 0; i <= n; i += 2, pass ^= 1) answer += (m + (pass || m == 1)) / 2;
  answer += !(n & 1);

  cout << answer << "\n";
}