using System;
 
class Program{
  static void Main(string[] args){
    string line = Console.ReadLine();
    string[] terms = line.Split(' ');
    long H = int.Parse(terms[0]);
    long W = int.Parse(terms[1]);
    if(H == 1 || W == 1){
      Console.WriteLine(1);
    }else{
      Console.WriteLine(H * W / 2 + H * W % 2);
    }
  }
}