#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<iomanip> #include<cmath> using namespace std; int main(){ int a; cin>>a; if(a<=2){ cout<<"6"; } else if(a>2 && a<=10){ cout<<6+(a-2)*1.8; } else{ cout<<6+(a-2)*1.8+(a-2-10)*(1.8+0.5); } return 0; }