void main() {
  problem();
}

void problem() {
  auto N = scan!ulong + 1;
  
  ulong solve() {
    ulong[] divisers = new ulong[N];
    divisers[] = 1;
    foreach(i; 2..N) {
      for(ulong x = i; x < N; x += i) divisers[x]++;
    }

    ulong ans;
    foreach(i; 1..N) ans += i * divisers[i];
    return ans;
  }

  solve().writeln;
}

// ----------------------------------------------

import std.stdio, std.conv, std.array, std.string, std.algorithm, std.container, std.range, core.stdc.stdlib, std.math, std.typecons, std.numeric;
T[][] combinations(T)(T[] s, in int m) {   if (!m) return [[]];   if (s.empty) return [];   return s[1 .. $].combinations(m - 1).map!(x => s[0] ~ x).array ~ s[1 .. $].combinations(m); }
string scan(){ static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res; }
T scan(T)(){ return scan.to!T; }
T[] scan(T)(int n){ return n.iota.map!(i => scan!T()).array; }
void deb(T ...)(T t){ debug writeln(t); }
alias Queue = Tuple!(long, "from", long, "to");

// -----------------------------------------------
