def main():
    N, I = map(int, input().split())
    salt_taste_list = []
    for _ in range(N):
        salt_taste_list.append(tuple(map(int, input().split())))

    salt_taste_list.sort(key=lambda ramen: ramen[1]/ramen[0], reverse=True)
    current_taste = 0
    current_salt = 0
    for ramen in salt_taste_list:
        if current_salt > I:
            raise ValueError
        if current_salt == I:
            break

        if current_salt + ramen[0] <= I:
            current_taste += ramen[1]
            current_salt += ramen[0]

    print(current_taste)


if __name__ == "__main__":
    main()