'use strict'
function main(inp) {
  inp = inp.trim().split(' ').map(x => x*1);
  
  let ans = 1;
  if(inp[0] != 1 && inp[1] != 1){
	ans = Math.ceil((inp[0]*inp[1])/2);
  }
  console.log(ans);
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'));
