codeforces 50A

http://codeforces.com/problemset/problem/50/A

#include<cstdio>
#include<iostream>
using namespace std;
int main()
{
int n,m,i;
while(cin>>m>>n)
{
if(n%2==0)
cout<<m*n/2<<endl;
else
cout<<m*(n/2)+m/2<<endl;
}
return 0;
}