We will buy a product for N yen (the currency of Japan) at a shop.  If we use only 1000-yen bills to pay the price, how much change will we receive?  Assume we use the minimum number of bills required.
N = int(open(0).read())
print(N % 1000)

N = int(open(0).read())
m = N % 1000
if m == 0:
    print(0)
else:
    print(1000 - m)