#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; cin>>a; if(a<=2){ cout<<6; } else if(a>=2&&a<=10){ cout<<6+1.8*(a-2); }else{ cout<<6+1.8*8+1.8*(1+0.5)*(a-10); } return 0; }