program Project1;

{$APPTYPE CONSOLE}


 var
a,b,n,r,c,k: longint ;
l:real;
 f1,f2:text;


begin

assign(f1,'photo.dat');
reset(f1);
readln(f1,n,a,b,r);
assign(f2,'photo.sol');
rewrite(f2);
while n>c do
begin
c:=c*2;
k:=k+1
end;
l:=a*b/sqr(2.54)*sqr(r)*k/8/1024 ;
writeln(f2,L:2:2);
close(f1);
close(f2);
end.