#include <iostream>
using namespace std;

int n,m;

int main(){
    cin>>n>>m;
    if (n>m)
        swap(n,m);
    if (n==2 && m==2){
        cout<<4<<endl;
        return 0;
    }
    if (n==2 && m==3){
        cout<<4<<endl;
        return 0;
    }
    if (n==1 || m==1){
        cout<<n*m<<endl;
        return 0;
    }
    if ((n*m%2)==0)
        cout<<(n*m)/2<<endl;
    else
        cout<<(n*m)/2+1<<endl;
    return 0;
}