#include <bits/stdc++.h>
using namespace std;
 
 
int a,b;
 
void init(){
cin>>a;
cin>>b;
 
}
void solve(){
    int dem = b / 3 - (a - 1) / 3;
    cout << dem;
}
 
int main(){
init();
solve();
return 0;
 
}
 
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