#!/usr/bin/perl -w

use strict;

select((select(STDOUT), $| = 1)[0]);

my $sum = 0;

my $d = 0;

for (my $exp = 1;; $exp++) {

$sum += ((-1) ** ($exp + 1)) / (2 * $exp - 1);

$d++;

if (0 == $d % 1000000) {

print "".(4 * $sum)."\r";

$d = 0;

}

}