import std.stdio, std.string, std.algorithm, std.array, std.range, std.conv,
    std.typecons, std.math, std.container, std.format, std.numeric;

void main(string[] args)
{
    long n;
    readf("%d\n", &n);
    n++;

    // ふるいをやるんだけど、各値についてその素因数を記録しておく
    long[] factorcount = new long[](n);
    factorcount[0] = 0;
    factorcount[1] = 1;

    long ans = 1;
    for (long i = 2; i < n; i++)
    {
        ans += i * (factorcount[i] + 2);
        for (long j = i + i; j < n; j += i)
        {
            factorcount[j] += 1;
        }
    }
    writeln(ans);

}
