#include<iostream>
using namespace std;
int main()
{
  	int 1<=H,1<=W,x,y,p;
  	double z;
  
  cin>>H>>W;
  x=H*W;
  y=x%2;
  z=x/2;
  p=z+0.5;
  if(H==1||W==1)
    cout<<1;
  
 
  else
  	if(y==0)
   	 	cout<<z;
 	 else
    	cout<<p;
}