#include<bits/stdc++.h>
using namespace std;
int main(){
int n;
cin>>n;
int res=n;//初始瓶盖
int ans=n;//总共喝了多少瓶
while(res>=3){//瓶盖数大于等于3一直循环
int t;
t=res/3;
ans+=t;
res=t+res%3;
}
cout<<ans<<endl;
return 0;
}