#include <bits/stdc++.h>
using namespace std;
int main(){
   int i;
   cin>>i;
   double s,t,a;
   cin>>a;
   if(i<=40){
     t=i*a;
   }else if(i>40&&i<=50){
     s=i-40;
     t=a*40+a*1.5*s;
   }else if(i>50){
     s=i-50;
     t=a*40+a*1.5*10+a*2*s;
   }
   printf("%.2f",t);
}
/**************************************************************
	Problem: 1860
	User: linmiaoling
	Language: C++
	Result: Accepted
	Time:51 ms
	Memory:2072 kb
****************************************************************/