#include <bits/stdc++.h>

using namespace std;

long long n,suma,kontor,p,d,s;

long long putere (long long a, long long b)
{
	p=1;
	for(int i=0;b>0;++i)
    {
		if((b & (1<<i))!=0)
			b^=(1<<i),p=p*a;
		a=a*a;
	}
	return p;
}

long long f (long long nr)
{
	d=2;s=1;
	while(nr>1)
    {
		kontor=0;
		while(nr%d==0)
			++kontor,nr/=d;
		if(kontor>0)
			s=s*(d-1)*putere(d,kontor-1);
		++d;
		if(d*d>nr)
			d=nr;
	}
	return s;
}

int main ()
{
	long long ans=1;
	freopen("fractii.in","r",stdin);
	freopen("fractii.out","w",stdout);
	scanf("%lld", &n);
	for(long long i=2;i<=n;++i)
    {
		ans=ans+2*f(i);
	}
	printf("%lld", ans);
	return 0;
}