#include<iostream>
#include<cstring>
using namespace std;
int main(){
long long a,b,i,r,f=1;
cin>>a>>b;
if(a>b){
r=a;
i=b;
}else{
r=b;
i=a;
}
if(a==b){
    cout<<1;
}else{
    if((a==b-1 or a==b+1)or ((a==3 and b==5) or (a==5 and b==3))){
cout<<(a*b)/4+1-2*((r-i)-1);
}else{
while(f!=1 and f!=b and f!=a*b-a and f!=a*b){







}




}
}
return 0;
}