#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int N=1e7+10;
ll n,ans,cnt,k;
ll pri[N],sum[N],phi[N];
bool st[N];
void prime(ll x){
	ll t;
	phi[1]=1;
	for(ll i=2;i<=n;i++){
		if(!st[i]){
			pri[cnt++]=i;
			phi[i]=i-1;
		}
		t=x/i;
		for(ll j=0;pri[j]<=t;j++){
			st[pri[j]*i]=1;
			if(i%pri[j]==0){
				phi[pri[j]*i]=phi[i]*pri[j];
				break;
			}
			phi[pri[j]*i]=phi[i]*(pri[j]-1);
		}
	}
	for(int i=1;i<=n;i++){
		sum[i]=sum[i-1]+phi[i];
	}
	return;
}
int main(){
	freopen("gcd_prime.in","r",stdin);
	freopen("gcd_prime.out","w",stdout);
	scanf("%lld",&n);
	prime(n);
	for(ll i=0;i<cnt;i++){
		k=n/pri[i];
		if(k>=1) ans+=2*sum[k]-1;
	}
	printf("%lld",ans);
	return 0;
}