x, y, d = [ int(v) for v in input().split(" ") ]

c = x + y - d + 1

if x >= d and y >= d:
	print(d+1)
elif x >= d:
	print(d-y)
elif y >= d:
	print(d-x)
elif c < 0:
	print(0)
else:
	print(c)