#include<stdio.h>
int v[1000010],i,j,n;
long long sol;
int main()
{
    freopen("fractii.in","r",stdin);
	freopen("fractii.out","w",stdout);
	scanf("%d",&n);
    sol=1;
    for (i=1;i<=n;++i)
	{
        v[i]=i;
    }
    for(i=2;i<=n;++i)
	{
        if (v[i]==i)
		{
            for (j=i;j<=n;j+=i)
			{
                v[j]=v[j]/i*(i-1);
            }
        }
        sol+=2*v[i];
    }
    printf("%lld",sol);
    return 0;
}