fscanf(STDIN, "%d %d %d", $A, $B, $S);


$ans = 0;

if($A == 0){
$ans += 1; 	
}

if(abs($S-$A) <= abs($S-$B) && $A>=$S ){
	$ans += $A;
}elseif(abs($S-$A) > abs($S-$B) && $B>=$S && $B>$A){
	$ans += $B;
}elseif(abs($S-$A) <= abs($S-$B) && $S>=$A){
	$ans += abs($S-$A) + $S;
}elseif(abs($S-$A) > abs($S-$B) && $S>$B && $B>$A){
	$ans += abs($S-$B) + $S;
}elseif(abs($S-$A) > abs($S-$B) && $B>$S && $A>$S){
	if($A - $S*2 +1 > 0){
		$ans += $A + $B -1;
	}else{
		$ans += $A *2 + $B -$S*2;
	}	
}

echo $ans;