题解 | #汽水瓶#

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


int main(){
    int n;
    while(cin>>n&&n!=0){
        int nums=0;
        while(n>2){
            int t = n/3;
            nums+=t;
            n = n%3+t;
        }
        if(n==2)
            nums++;
        cout<<nums<<endl;
    }
    return 0;
}