#!/usr/bin/perl -w

$coin_toss=1000; # =n
$toss_side1=60; # =k

$total_p=0;
foreach($toss_side1..$coin_toss)
	{
	# calculate factorials
	$n_fac=fac($coin_toss);
	$n_minus_k_fac=fac($coin_toss-$_);
	$k_fac=fac($_);
	
	# calculate propability for getting side 1 exactly $_ times
	$partial_p=($n_fac/($n_minus_k_fac*$k_fac))*(0.5**$_)*(0.5**($coin_toss-$_));
	
	# add propability to total propapility
	$total_p=$total_p+$partial_p;
	}
print"Propability to get side 1 at least $toss_side1 times tossing a coin $coin_toss times: $total_p\n";
system("pause");
exit;

# subroutine for calculating factorials
sub fac
	{
	$_[0]>1?$_[0]*fac($_[0]-1):1;
	}