"use strict"
function Main(stdin){
stdin = stdin.trim().split("\n").reverse();
let stdout = [];
function input(){return stdin.pop()};
function print(x){stdout.push(x)};
function max(list){return list.reduce(function(a,b){ return Math.max(a,b) }) }
function min(list){return list.reduce(function(a,b){ return Math.min(a,b) }) }
function sum(list){return list.reduce(function(a,b){ return a+b }) }
function sortex(list, index){list.sort((a, b) => a[index] - b[index])}
function all(list){return list.reduce(function(a,b){ return a && b }) }
function any(list){return list.reduce(function(a,b){ return a || b }) }
/*START*/


let tmp = Array.from(input().split(" "), i => parseInt(i))
let a = tmp[0]
let b = tmp[1]
if (a === 1 || b === 1){
    print(1)
}else{
    print(Math.floor((a*b + 1)/2))
}



/*END*/
console.log(stdout.join("\n"));
return stdout
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"))