#include<bits/stdc++.h> using namespace std; double x,y; int main(){ cin>>x>>y; if(x<40){ cout<<setprecision(2)<<fixed<<x*y; }else if(x<50){ cout<<setprecision(2)<<fixed<<40*y+(x-40)*(y*1.5); }else{ cout<<setprecision(2)<<fixed<<40*y+10*(y*1.5)+(x-50)*(y*2); } return 0; }