import sys


N = input()
    

N_in = int(N)

if N_in>10000 or N_in<0:
    print('error')
    sys.exit()

N = N_in/1000;

N_f = float(N)

N_i = int(N)


if (N_f - N_i) == 0:
    Ans = 0
    print(Ans)

else:
    N_i = N_i + 1
    Ans = N_i*1000 - N_in
    print(Ans)