import sys
input=lambda: sys.stdin.readline().rstrip()
x,y,d=map(int,input().split())
if x>y:
  x,y=y,x
if d<=x:
  print(d+1)
elif d<=y:
  print(x+1)
elif d<=x+y:
  print(x+y-d+1)
else:
  print(0)