#include<bits/stdc++.h> using namespace std; int main(){ double a,n; cin>>a; n = a-10; if(a <= 2){ cout<<6; }else{ if(a > 2 && a <= 10){ cout<<6+(a-2)*1.8; }else{ if(a > 10){ cout<<6+(a-2-n)*1.8+n*(1.8*(1+0.5)); } } } return 0; }