def main():
    l, r, n = map(int, input().split())

    l_rest = l % n
    if l_rest == 0:
        l_rest = n
    r_rest = r % n

    l_set_start = l + (n - l_rest)
    r_set_end = r - r_rest

    if l_set_start < r_set_end:
        print(n)
        return

    if l_set_start > r_set_end:
        print(r-l+1)
        return

    print(min(n-l_rest+r_rest+1, n))


if __name__ == "__main__":
    main()