Problem:
Score : 100 points

Problem Statement

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.

Constraints

1 \leq N \leq 10000

N is an integer.

Input

Input is given from Standard Input in the following format:

N

Output

Print the amount of change as an integer.

Sample Input 1

1900

Sample Output 1

100

We will use two 1000-yen bills to pay the price and receive 100 yen in change.

Sample Input 2

3000

Sample Output 2

0

We can pay the exact price.

Solution in OCaml (4.10.0) (judge verdict: Accepted)

let n = read_int ();;

let amount n = let rec iter result m = 
                        if m > result then iter (result+1000) m
                        else -(m - result)
                      in iter 1000 n;;

Printf.printf "%d\n" (amount n);;