#include<bits/stdc++.h>
using namespace std;
unsigned long long pr[40005],eu[40005],qz[40005],pn;
bool p[40005];
void euler(int n)
{
	long long k=0;
	eu[1]=1;
	for(int i=2;i<=n;++i)
	{
		if(!p[i])pr[++pn]=i,eu[i]=i-1;
		for(int j=1;j<=pn&&k<=n;++j)
		{
			k=i*pr[j];
			p[k]=1;
			if(i%pr[j]==0)
			{
				eu[k]=eu[i]*pr[j];
				break;
			}
			eu[k]=(pr[j]-1)*eu[i];
		}
	}
}
int main()
{
	euler(40005);
	for(int i=1;i<=40005;++i)
		qz[i]=qz[i-1]+eu[i];
	int n;
	cin>>n;
	if(n==0)cout<<0;
	else cout<<qz[n-1]*2+1;
	return 0;
}

求助qaq