#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int a,b=0; cin>>a; if(a<=2){ cout<<6; } else if(a>2 && a<=10){ printf("%.1f",6+(a-2)*1.8); } else{ printf("%.1f",(6+(10-2)*1.8)+(a-10)*(1.8+1.8*0.5)); } return 0; }