#include <stdio.h>
int main()
{
	long long n,i,j,s;
	int e[1000005];
	s=1;
	FILE *f1,*f2;
	f1=fopen("fractii.in","r");
	f2=fopen("fractii.out","w");
	fscanf(f1,"%lld",&n);
	for(i=1;i<=n;i++)
	{
		e[i]=i;
	}
	for(i=2;i<=n;i++)
	{
		if(e[i]==i)
		{
			for(j=i;j<=n;j=j+i)
				e[j]=e[j]/i*(i-1);
		}
	}
	for(i=2;i<=n;i++)
	{
		s=s+2*e[i];
	}
	fprintf(f2,"%lld",s);
	fclose(f1);
	fclose(f2);


	return 0;
}