// yukicoder: No.135 とりあえず1次元の問題
// 2019.4.11 bal4u

#include <stdio.h>
#include <stdlib.h>

#define ABS(x) ((x)>=0?(x):-(x))

int main()
{
	int x, y, d, x0, y0, x1, y1, a, ans;

	scanf("%d%d%d", &x, &y, &d);
	if (x + y < d) ans = 0;
	else {
		if (d <= y) x0 = 0, y0 = d;
		else x0 = d - y, y0 = y;
		if (d <= x) x1 = d, y1 = 0;
		else x1 = x, y1 = d - x;
		ans = ABS(x1 - x0) + 1;
		a = ABS(y1 - y0) + 1;
		if (a < ans) ans = a;
	}
	printf("%d\n", ans);
	return 0;
}