#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;
const int maxn=1e7+7;
long long prime[maxn],phi[maxn],n,totprime;
long long ans=0;
bool vis[maxn];
int main()
{
	scanf("%lld",&n);
	phi[1]=1;
	for (int i=2;i<=n;i++)
	{
		if (!phi[i])
		{
			prime[totprime++]=i;
			phi[i]=i-1;
		}
		for (int j=0;j<totprime&&i*prime[j]<=n;j++)
		{
			if (i%prime[j])
				phi[i*prime[j]]=phi[i]*(prime[j]-1);
			else
			{
				phi[i*prime[j]]=phi[i]*prime[j];
				break;
			}
		}
	}
	for (int i=2;i<=n;i++)
		phi[i]+=phi[i-1];
	for (int i=0;i<totprime;i++)
		ans+=phi[n/prime[i]]*2-1;
	printf("%lld\n",ans);
	return 0;
}