#include<bits/stdc++.h>
using namespace std;

int main(){
	cin.tie(0),ios::sync_with_stdio(false);
	int a,b; cin>>a>>b;
	int rem=(a+b)%3;
	int l=a; while(l<=b&&(l+rem)%3)++l;
	int r=b; while(r>=a&&(r+rem)%3)--r;
	int ans=(r-l)/3;
	cout<<max(0,ans+1)<<"\n"s;
}