#include <bits/stdc++.h>

using namespace std;
int n,v[1000006];long long ans;
int main () {
	freopen("fractii.in","r",stdin);
	freopen("fractii.out","w",stdout);
	scanf("%d", &n);
	ans=1;
	for(int i=1;i<=n;++i)
		v[i]=i;
	for(int i=2;i<=n;++i) {
		if(v[i]==i) {
			for(int j=2;j*i<=n;++j)
				v[i*j]=v[i*j]/i*(i-1);
		}
		ans=ans+2*v[i];
	}
	printf("%lld", ans);
	return 0;
}