#include<bits/stdc++.h>
using namespace std;
const int N=1e7+5;
int n,m,p[N],phi[N];
long long sum[N],ans;
bool isp[N];
void eular(int n) {
	phi[1]=1;
	for(int i=2;i<=n;++i) {
		if(!isp[i]) p[++m]=i,phi[i]=i-1;
		for(int j=1;j<=m&&i*p[j]<=n;++j) {
			isp[i*p[j]]=1;
			if(i%p[j]==0) {
				phi[i*p[j]]=phi[i]*p[j];
				break;
			} else {
				phi[i*p[j]]=phi[i]*phi[p[j]];
			}
		}
	}
	for(int i=1;i<=n;++i) sum[i]=sum[i-1]+phi[i];
}
int main() {
	freopen("gcd_prime.in","r",stdin);
	freopen("gcd_prime.out","w",stdout);
	scanf("%d",&n);
	eular(n);
	for(int i=1;i<=m;++i) ans+=2*sum[n/p[i]]-1;
	printf("%lld",ans);
	return 0;
}