/* Bismillahir Rahmanir Rahim. */
#include<bits/stdc++.h>
using namespace std;
typedef long long ll
#define SET(n,k) (n|(1<<k))
#define CHECK(n,k) (n&(1<<k))



int main() {
	ios_base::sync_with_stdio(false);
	// #ifndef ONLINE_JUDGE
	// freopen("input.txt", "r", stdin);
	// freopen("output.txt", "w", stdout);
	// #endif
	ll r,h;
	cin>>r>>h;
	cout<<(r*h+1)/2<<endl;
	return 0;
}