#include<bits/stdc++.h>
using namespace std;
int main(){
   int a,b;
   int sum1,sum2,small,great;
   cin>>a>>b;

   if(a==0||b==0||a==b){
    cout<<"NO"<<endl;
   }

   else {
        if(a<b){
         small=a;
         great=b;
        }
   else {
    small=b;
    great=a;
   }
   for(int i=small;i<=great;i++){
    sum1=abs(a-i);
    sum2=abs(b-i);
    if(sum1==sum2){
        cout<<i<<endl;

    }


   }
   }



}
