#include <cstdlib>
#include <iostream>

#include <typeinfo>
using namespace std;
int main(){
int a,b;
cin>>a>>b;
int count=0;
for(int i=a;i<b+1;i++){
    if ((a+b+i)%3==0){
        count+=1;
    }
}
cout<<count<<endl;
}