题解

#include<bits/stdc++.h>
using namespace std;
int a,n,num,sum;
int main(){
    cin>>a;
    n=a;
    while(n>=3){
        num=num+n/3;
        n%=3;
        n+=num;
        sum+=num;
        num=0;
    }
    cout<<sum+a;
    return 0;
}