3283. 食堂的座位

include

using namespace std;
int main(){
int n,m;
cin>>n>>m;
int sum=(m/2)*n;
if(m%2==1&&n%2==1){
sum+=n/2+1;
}
else if(m%2==1&&n%2==0){
sum+=n/2;
}
cout<<sum<<endl;
return 0;
}