#include<bits/stdc++.h>
#define endl "\n"
using namespace std;
#define ll long long
#define ld long double
#define ui unsigned int
#define ull unsigned ll
#define foi(n) for(ll i=0;i<n;i++)
#define foj(n) for(ll j=0;j<n;j++)
#define fok(n) for(ll k=0;k<n;k++)
#pragma GCC optimize("O3", "unroll-loops")
#define fixed(); cout << fixed << setprecision(20);
#define fast(); ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);

/*****************************************************************************/


#define graph          vector<vector<int>>
#define V              vector
typedef pair<int, int> pii;
typedef pair<ll, ll>   pll;
typedef V<int>         vi;
typedef V<ll>          vll;
typedef V<string>      vs;
typedef V<double>      vd;
typedef V<pii>         vpii;             
typedef V<pll>         vpll;             
typedef pair<int,pii>  piii;             
typedef priority_queue<pii, vector<pii>, greater<pii> > pqq;   

/*****************************************************************************/

#define mp                   make_pair
#define eb                   emplace_back
#define pb                   push_back
#define pf                   push_front
#define popb                 pop_back
#define popf                 pop_front
#define hashmap              unordered_map
#define hashset              unordered_set
#define lb                   lower_bound
#define ub                   upper_bound
#define all(a)               (a).begin(), (a).end()
#define rall(a)              (a).rbegin(), (a).rend()
#define ff                   first
#define ss                   second
#define lbpos(v,x)           (int)(lower_bound(all(v),x)-v.begin())//=v.size()==>No LB 
#define ubpos(v,x)           (int)(upper_bound(all(v),x)-v.begin())//=v.size()==>No UB

/*****************************************************************************/

//for declaring most used global variables and constants
ll mod=1e9+7;

//For Calculating nCr
template<typename T>
T nCr(T n, T r) {
    if(r > n - r) r = n - r; // because C(n, r) == C(n, n - r)
    int  ans = 1,i;
    for(i = 1; i <= r; i++) {
        ans *= n - r + i;
        ans /= i;
    } return ans;
}

//power optimized
template<typename T,typename T2>
T2 power(T x, T y) 
{ 
    if (y == 0)  return 1; 
    T2 res=power(x,y/2);
    if (y % 2)  return res*res*x;
    return res*res; 
}

//return number of set bits in a given number
template<typename T>
ll countSetBits(T n) 
{ 
    return __builtin_popcount (n);
}

//return true if number is prime
template<typename T>
bool isPrime(T n) 
{ 
    // Corner cases 
    if (n <= 1)  return false; 
    if (n <= 3)  return true; 
    if (n % 2 == 0 || n % 3 == 0)  return false; 
    for (ll i = 5; i * i <= n; i = i + 6) 
        if (n % i == 0 || n % (i + 2) == 0) 
            return false; 
   return true; 
} 

//return true if string is palindrome
bool ispalindrome(string s)
{
    ll len=s.length();
    foi(len){
        if(s[i]!=s[len-i-1])
        return false;
    }
    return true;
}

//for string with space use std::getline(cin,string_name);
//*****************UVAISH ZAFRI(Rush_For_AC)**********************

int32_t main() {
    fast();fixed();
    #ifndef ONLINE_JUDGE
    freopen("input.txt","r",stdin);
    freopen("output.txt","w",stdout);
    #endif
  
  
  double n;
  cin>>n;
  ll res=0;
  for(double k=1;k<=n;k++)
  res+=(((double)k/2.0F) * floor(n/(double)k) * floor(1.0F + (n/(double)k)));
  cout<<res<<endl;
  
}


Measured memory_bytes: 3748