#!/usr/bin/evn perl

use strict;
use warnings;

my $c = <>;
my ($ri, $ro) = split / /, <>;
my $pi = 3.14159265359;
my $r = ($ro - $ri) / 2 + $ri;
my $s = $pi * ($r - $ri) ** 2;
my $l = 2 * $pi * $r;
my $v = $s * $l;
my $ans = $v * $c;
print "$ans\n";

exit;