#include <cstdio>
#define N 1000000
int n,e[N];
void read(){
	freopen("fractii.in","r",stdin);
	scanf("%d",&n);
}
void solve(){
	int i,j;
	for (i=1;i<=n;++i)
		e[i]=i;
	for (i=2;i<=n;++i)
		if (e[i]==i)
		{
			--e[i];
			for (j=i+i;j<=n;j+=i)
				e[j]=e[j]*(i-1)/i;
		}
}
void write(){
	int i;
	long long sum=1;
	freopen("fractii.out","w",stdout);
	for (i=2;i<=n;++i)
		sum+=2*e[i];
	printf("%lld\n",sum);
}
int main(){
	read();
	solve();
	write();
}