#include<iostream> #include<cstdio> using namespace std; int main(){ int a; cin>>a; if(a<=2){ cout<<"6"; } else if(10>=a>2){ cout<<6+1.8*(a-2); } else if(a>10){ cout<<6+8*1.8+((1.8+1.8*0.5)*(a-10)); } return 0; }