#include<bits/stdc++.h>
using namespace std;
using Int = long long;
//INSERT ABOVE HERE
signed main(){
  Int a,b;
  cin>>a>>b;
  Int ans=0;
  for(Int i=a;i<=b;i++)
    ans+=(a+b+i)%3==0;
  cout<<ans<<endl;
  return 0;
}