#include<iostream>
using namespace std;
int main(){
    int n,m;
    cin>>n;
    int res=n+n/3;
     m=n/3;
     n=n%3+m;
    while(m){
        m=n/3;
        res+=m;
        n=n%3+m;
    }
    cout<<res<<endl;
    return 0;
}