import sys

read = sys.stdin.read

readline = sys.stdin.readline

readlines = sys.stdin.readlines



def main(N):

    ans = 0



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

        ans += (N // n) * n * (1 + (N // n)) // 2



    print(ans)





if __name__ == "__main__":

    N = int(readline())

    main(N)

from numba import njit

import sys

read = sys.stdin.read

readline = sys.stdin.readline

readlines = sys.stdin.readlines



@njit

def main(N):

    ans = 0



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

        ans += (N // n) * n * (1 + (N // n)) // 2



    print(ans)





if __name__ == "__main__":

    N = int(readline())

    main(N)

import sys

read = sys.stdin.read
readline = sys.stdin.readline
readlines = sys.stdin.readlines


def main(N):
    ans = 0
    for n in range(1, N + 1):
        ans += (N // n) * n * (1 + (N // n)) // 2
    print(ans)


if __name__ == "__main__":
    N = int(readline())
    main(N)

from numba import njit
import sys

read = sys.stdin.read
readline = sys.stdin.readline
readlines = sys.stdin.readlines


@njit
def main(N):
    ans = 0
    for n in range(1, N + 1):
        ans += (N // n) * n * (1 + (N // n)) // 2
    print(ans)


if __name__ == "__main__":
    N = int(readline())
    main(N)

+from numba import njit +@njit