【題目敘述】https://atcoder.jp/contests/panasonic2020/tasks/panasonic2020_b
#include <bits/stdc++.h>
using namespace std;
long long n, m, ans;
int main(){
cin >> n >> m;
if (n == 1 || m == 1) ans = 1;
else ans = (n*m+1)/2;
cout << ans << "\n";
}