#coding: utf-8
##yuki_131

s=map(int,raw_input().split())

x=int(s[0])
y=int(s[1])
d=int(s[2])

if x<y:
 x,y=y,x

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