#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: wangyiyang
	Language: C++
	Result: Accepted
	Time:43 ms
	Memory:2072 kb
****************************************************************/