#!/usr/bin/perl

use strict;
use warnings;

my ($x, $y, $d) = split / /, <>;
my $count;

if($y < $x) {
	($x, $y) = ($y, $x);
}

if(($x <= $d)and($d <= $y)) {
	$count = $x;
} elsif($d < $x) {
	$count = $x;
} elsif($x + $y < $d) {
	$count = 0;
} elsif(($y < $d)and($d <= $y + $x)) {
	$count = $y + $x - $d + 1;
} 

print "$count\n";

exit;