#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> ii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<vi> vvi;
typedef vector<vii> vvii;
#define fi first
#define se second
#define ALL(x) (x).begin(), (x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define eb emplace_back
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define SZ(x) (int)(x).size()
#define endl '\n'
#define FOR(a, b, c) for (auto a = (b); (a) < (c); ++(a))
#define F0R(a, b) FOR (a, 0, (b))
#define CEIL(a, b) ((a) + (b)-1) / (b)
template <class T>
bool ckmin(T& a, const T& b) {
  return a > b ? a = b, true : false;
}
template <class T>
bool ckmax(T& a, const T& b) {
  return a < b ? a = b, true : false;
}
#ifndef DEBUG
#define DEBUG 0
#endif
#define dout \
  if (DEBUG) std::cerr
#define dvar(...) " [" << #__VA_ARGS__ ": " << mt(__VA_ARGS__) << "] "
template <typename T>
struct IsC {
  template <typename C>
  static char test(typename C::const_iterator*);
  template <typename C>
  static int test(...);
  static const bool value = sizeof(test<T>(0)) == sizeof(char);
};
template <>
struct IsC<string> {
  static const bool value = false;
};
template <typename C>
typename enable_if<IsC<C>::value, ostream&>::type operator<<(ostream&, const C&);
template <typename T1, typename T2>
ostream& operator<<(ostream&, const pair<T1, T2>&);
template <typename... T> using TS = tuple_size<tuple<T...>>;
template<size_t idx, typename... T>
typename enable_if<TS<T...>::value == idx + 1, ostream&>::type
operator<<(ostream& o, const tuple<T...>& t) {
  return o << ", " << get<idx>(t) << ')';
}
template<size_t idx, typename... T>
typename enable_if<0 < idx && idx + 1 < TS<T...>::value, ostream&>::type
operator<<(ostream& o, const tuple<T...>& t) {
  return operator<<<idx + 1>(o << ", " << get<idx>(t), t);
}
template<size_t idx = 0, typename... T>
typename enable_if<1 < TS<T...>::value && !idx, ostream&>::type
operator<<(ostream& o, const tuple<T...>& t) {
  return operator<<<idx + 1>(o << '(' << get<idx>(t), t);
}
template<typename T>
ostream& operator<<(ostream& o, const tuple<T>& t) {
  return o << get<0>(t);
}
template <typename T1, typename T2>
ostream& operator<<(ostream& o, const pair<T1, T2>& p) {
  return o << mt(p.fi, p.se);
}
template <typename C>
typename enable_if<IsC<C>::value, ostream&>::type operator<<(
    ostream& o, const C& c) {
  o << '[';
  for (auto it = c.cbegin(); it != c.cend(); ++it)
    o << *it << (next(it) != c.cend() ? ", " : "");
  return o << ']';
}
template <typename T>
void tprint(vector<vector<T>>& v, size_t width = 0, ostream& o = cerr) {
  if (!DEBUG) return;
  for (auto& vv : v) {
    for (auto& i : vv) o << setw(width) << i;
    o << endl;
  }
}

const int mxN = (int)1e7;
int lp[mxN+1];
vector<int> pr;
void pre() {
  for (int i=2; i<=mxN; ++i) {
    if (lp[i] == 0) {
      lp[i] = i;
      pr.push_back (i);
    }
    for (int j=0; j<(int)pr.size() && pr[j]<=lp[i] && i*pr[j]<=mxN; ++j)
      lp[i * pr[j]] = pr[j];
  }
}

void solve() {
  ll n;
  cin >> n;
  ll ans = 1;
  for (ll i = 2; i <= n; ++i) {
    ll cnt = 1;
    ll j = i;
    ll last = -1;
    ll lastnew = -1;
    while (j > 1) {
      if (last != lp[j]) {
        last = lp[j];
        lastnew = cnt;
      }
      cnt += lastnew;
      j /= lp[j];
    }
    ans += i * cnt;
  }
  cout << ans << endl;
}

int main() {
  ios_base::sync_with_stdio(0);
  cout.tie(0);

  pre();
  int tt = 1;
  FOR (t, 1, tt + 1) {
    // cout << "Case #" << t << ": ";
    solve();
  }
  
  return 0;
}


Measured memory_bytes: 46452