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