#include<cstdio>
#define maxn 50000
using namespace std;
int s[maxn+100]={0};
long long sum=0,n;
bool vis[maxn+100]={0};
void Euler();
int main(){
	freopen("sendtable.in","r",stdin);
	freopen("sendtable.out","w",stdout);
	scanf("%d",&n);
	Euler();
	for (int i=2;i<=n;i++){
		sum+=s[i];
	}
	printf("%lld",sum*2+1);
	return 0;
}
void Euler(){
	for (int i=1;i<=n;i++) s[i]=i;
	for (int i=2;i<=n;i++) if (!vis[i]) {
		for (int j=i;j<=n;j+=i){
			s[j]=(s[j]/i)*(i-1);
			vis[j]=1;
		}
	}
	return;
}