# coding: utf-8

# Your code here!

import sys

read = sys.stdin.read

readline = sys.stdin.readline



n, = list(map(int,readline().split()))



ans = 0

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

    ans += (i+i*(n//i))*(n//i)//2

print(ans)

def F(N): 

    r = int(N**0.5) # x >= 10^9 のときは注意

    ans = 0

    for d in range(1,N//r+1):

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



    #print(ans)    

    for c in range(1,r):

        a = N//(c+1)

        b = N//c

        """

        (a,b] 上で d の和を求める

        """

        s = b*(b+1)//2-a*(a+1)//2

        ans += s*(c*c+c)//2

        #ans %= MOD

    return ans





# coding: utf-8

# Your code here!

import sys

read = sys.stdin.read

readline = sys.stdin.readline



n, = list(map(int,readline().split()))

print((F(n)))







# coding: utf-8
# Your code here!
import sys

read = sys.stdin.read
readline = sys.stdin.readline
(n,) = list(map(int, readline().split()))
ans = 0
for i in range(1, n + 1):
    ans += (i + i * (n // i)) * (n // i) // 2
print(ans)

def F(N):
    r = int(N**0.5)  # x >= 10^9 のときは注意
    ans = 0
    for d in range(1, N // r + 1):
        ans += d * (1 + (N // d)) * (N // d) // 2
    # print(ans)
    for c in range(1, r):
        a = N // (c + 1)
        b = N // c
        """
        (a,b] 上で d の和を求める
        """
        s = b * (b + 1) // 2 - a * (a + 1) // 2
        ans += s * (c * c + c) // 2
        # ans %= MOD
    return ans


# coding: utf-8
# Your code here!
import sys

read = sys.stdin.read
readline = sys.stdin.readline
(n,) = list(map(int, readline().split()))
print((F(n)))

+def F(N): +    r = int(N**0.5)  # x >= 10^9 のときは注意 +    ans = 0 +    for d in range(1, N // r + 1): +        ans += d * (1 + (N // d)) * (N // d) // 2 +    # print(ans) +    for c in range(1, r): +        a = N // (c + 1) +        b = N // c +        """ +        (a,b] 上で d の和を求める +        """ +        s = b * (b + 1) // 2 - a * (a + 1) // 2 +        ans += s * (c * c + c) // 2 +        # ans %= MOD +    return ans + + -ans = 0 -for i in range(1, n + 1): -    ans += (i + i * (n // i)) * (n // i) // 2 -print(ans) +print((F(n)))