#include <fstream>
using namespace std;

long long solve(long long a)
{
    long long v[1000000], i, j, s=0LL;
    for (i=2;i<=a;i++) v[i]=i;
    for (i=2;i<=a;i++)
        if (v[i]==i)
            for (j=i;j<=a;j+=i)
                v[j]=v[j]/i*(i+1);
    for (i=2;i<=a;i++)
    s+=v[i];
    return s*2+1;
}

int main()
{
    long long a;
    fstream in ("fractii.in", iostream::in);
    fstream out ("fractii.out", iostream::out);
    in>>a;
    out<<solve(a);
    in.close();
    out.close();
    return 0;
}