x, y, d = map(int, input().split(" "))

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