// Slower C++ solution:
#include <iostream>

#include <iomanip>

#include <vector>

#include <set>

#include <string>

#include <queue>

#include <algorithm>

#include <map>

#include <cmath>

#include <numeric>

#include <list>

#include <stack>

#include <cstdio>

#include <cstdlib>

#include <cstring>

#include <tuple>

#include <deque>

#include <complex>



using namespace std;



/*

typedef vector<int> vi;

typedef vector<vi> vvi;

typedef pair<int, int> pii;

typedef vector<pii> vpii;

*/



typedef long long ll;

typedef vector<ll> vll;

typedef vector<vll> vvll;

typedef pair<long long, long long> pll;

typedef vector<pll> vpll;



typedef long double ld;

typedef vector<ld> vld;



typedef vector<bool> vb;



#define rep(i, n) for (ll i = 0; i < (n); i++)

#define reps(i, n) for (ll i = 1; i <= (n); i++)

#define rrep(i, n) for (ll i = (n) - 1; i >= 0; i--)

#define rreps(i, n) for (ll i = (n); i >= 1; i--)

#define all(v) (v).begin(), (v).end()



template <class T> void chmin(T& a, T b) { a = min(a, b);}

template <class T> void chmax(T& a, T b) { a = max(a, b);}



constexpr int INF = 1 << 30;

constexpr ll INFL = 1LL << 60;

constexpr ll MOD = 1000000007;

constexpr ld EPS = 1e-12;

ld PI = acos(-1.0);



void solve() {

    ll n;

    cin >> n;

    vll cnt(n + 1);

    ll ans = 0;

    for(ll i = 1; i <= n; i++) {

        for(ll j = i; j <= n; j += i) {

            cnt[j]++;

        }

        ans += i * cnt[i];

    }

    cout << ans << endl;

    return;

}



int main() {

    std::cin.tie(nullptr);

    std::ios_base::sync_with_stdio(false);

    cout << fixed << setprecision(15);

    solve();

}

// Faster C++ solution for the same problem (measured speedup: 2.6576505633472927x):
#include <iostream>

#include <iomanip>

#include <vector>

#include <set>

#include <string>

#include <queue>

#include <algorithm>

#include <map>

#include <cmath>

#include <numeric>

#include <list>

#include <stack>

#include <cstdio>

#include <cstdlib>

#include <cstring>

#include <tuple>

#include <deque>

#include <complex>



using namespace std;



/*

typedef vector<int> vi;

typedef vector<vi> vvi;

typedef pair<int, int> pii;

typedef vector<pii> vpii;

*/



typedef long long ll;

typedef vector<ll> vll;

typedef vector<vll> vvll;

typedef pair<long long, long long> pll;

typedef vector<pll> vpll;



typedef long double ld;

typedef vector<ld> vld;



typedef vector<bool> vb;



#define rep(i, n) for (ll i = 0; i < (n); i++)

#define reps(i, n) for (ll i = 1; i <= (n); i++)

#define rrep(i, n) for (ll i = (n) - 1; i >= 0; i--)

#define rreps(i, n) for (ll i = (n); i >= 1; i--)

#define all(v) (v).begin(), (v).end()



template <class T> void chmin(T& a, T b) { a = min(a, b);}

template <class T> void chmax(T& a, T b) { a = max(a, b);}



constexpr int INF = 1 << 30;

constexpr ll INFL = 1LL << 60;

constexpr ll MOD = 1000000007;

constexpr ld EPS = 1e-12;

ld PI = acos(-1.0);



void solve() {

    ll n;

    cin >> n;

    ll ans = 0;

    for(ll i = 1; i <= n; i++) {

        ll m = n / i;

        ans += m * (m + 1) / 2 * i;

    }

    cout << ans << endl;

    return;

}



int main() {

    std::cin.tie(nullptr);

    std::ios_base::sync_with_stdio(false);

    cout << fixed << setprecision(15);

    solve();

}