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

if x > y:
    
    y, x = x, y
    
if x >= d:
    print(d + 1)
    
elif y >= d:
    
    print(x + 1)
    
elif x + y >= d:
    
    print(x + y - d + 1)
    
else:
    
    print(0)