L, R, M = map(int, input().split())
if R - L + 1 >= M:
    print(M)
else:
    mod_L = L % M
    mod_R = R % M
    if mod_L <= mod_R:
        print(mod_R - mod_L + 1)
    else:
        print((M - mod_L) + mod_R + 1)