#include <bits/stdc++.h>
using namespace std;

int main()
{
	ll r,c,res;
	cin>>r>>c;
	//int res = (floor(float(r)/2)*floor(float(c)/2))+(ceil(float(r)/2)*ceil(float(c)/2));
	if(r%2==0)
	{
		res = c*(r/2);
	}
	else
	{
		res = c*(r/2) + (c+1)/2;
	}
	cout<<res;
}
