x,y,d=map(int,raw_input().split())
if x+y<d:
    print 0
    exit()

x1,y1=d,0
if d>x:
  x1,y1=x,d-x
x2,y2=0,d
if d > y:
  x2,y2=d-y,y

print abs(x1-x2)+1