"use strict"
function main(arg) {
	let a = arg.split(' ');
 
	let x = a[0];
	let y = a[1];
 
	let isoddX;
	let isoddY;
 
	if(x % 2 === 1) isoddX = true;
	if(y % 2 === 1) isoddY = true;
	
if(isoddX && isoddY)
{
	console.log(((Math.floor( x / 2) + 1) * (Math.floor(y/2) + 1)) +  Math.floor(x/2) * Math.floor(y/2));
}
else if(isoddX){
	console.log((Math.floor( y / 2)) * x);
 
}
else if(isoddY){
	console.log((Math.floor( x / 2)) * y);
 
}
else
{
	console.log((Math.floor( x / 2)) * y);
}
 
 
 
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));