#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
#define rep(i,s,e) for(int (i) = (s);(i) <= (e);(i)++)
int a,b;
int main(){
  cin >> a >> b;
  int ans = 0;
  rep(i,a,b){
    if((a + b + i) % 3 == 0){
      ans += 1;
    }
  }

  cout << ans << endl;
}