#131 manhattann distance
x,y,d=(int(i) for i in input().split())
if x+y<d:
    print(0)
else:
    if x>y:
        m=y
        t=x
    else:
        m=x
        t=y
    if d<m:
        print(d+1)
    elif d<=t:
        print(m+1)
    else:
        print(x+y-d+1)