program photo;
var bit,n,a,b,r:integer;
k:real;
f1,f2:text;

begin
assign(f1,'photo.dat');
reset(f1);
read(f1,n,a,b,r);
close(f1);
bit:=1;
n:=n-1;
while n>1 do begin
bit:=bit+1;
n:=n div 2;
end;
if n>2 then bit:=bit+1;
k:=(a/2.54)*(b/2.54)*r*r*bit/8/1024;
k:=int(k*100)/100;
assign(f2,'photo.sol');
rewrite(f2);
writeln(f2,k:2:2);
close(f2);


end.