#!python3



import sys

iim = lambda: list(map(int, sys.stdin.readline().rstrip().split()))



def resolve():

    N = int(eval(input()))



    ans = 0

    for i in range(1, N+1):

        j = N // i

        ans +=  i * j * (1+ j) // 2

    print(ans)



if __name__ == "__main__":

    resolve()

#!python3



import sys

iim = lambda: list(map(int, sys.stdin.readline().rstrip().split()))



def resolve():

    N = int(eval(input()))



    ans = 0

    N2 = N//2

    for i in range(1, N2+1):

        j = N // i

        ans +=  i * j * (1+ j) // 2

    ans += (N2+1 + N) * (N-N2) // 2

    print(ans)



if __name__ == "__main__":

    resolve()

#!python3
import sys

iim = lambda: list(map(int, sys.stdin.readline().rstrip().split()))


def resolve():
    N = int(eval(input()))
    ans = 0
    for i in range(1, N + 1):
        j = N // i
        ans += i * j * (1 + j) // 2
    print(ans)


if __name__ == "__main__":
    resolve()

#!python3
import sys

iim = lambda: list(map(int, sys.stdin.readline().rstrip().split()))


def resolve():
    N = int(eval(input()))
    ans = 0
    N2 = N // 2
    for i in range(1, N2 + 1):
        j = N // i
        ans += i * j * (1 + j) // 2
    ans += (N2 + 1 + N) * (N - N2) // 2
    print(ans)


if __name__ == "__main__":
    resolve()

-    for i in range(1, N + 1): +    N2 = N // 2 +    for i in range(1, N2 + 1): +    ans += (N2 + 1 + N) * (N - N2) // 2