C++

#include<iostream>
using namespace std;
int main(){

    int a,b=0,c=0;
    cin>>a;
    while((a+b)>=3){
        b=b+a;
        c=c+a;
        a=b/3;
        b=b-b/3*3;
    }
    cout<<c+a;
    
    return 0;
}