#include <cstdio>

using namespace std;
int v[1000000];
int ciur (int n)
{
    int i;
    for(i=2;i<=n;i++)
    {
        v[i]=i;
    }
    for (i=2;i<=n;i++)
    {
        if (v[i]==i)
        {
            for (int j=i;j<=n;j+=i)
            {
                v[j]=v[j]/i*(i-1);
            }
        }
    }
}

int main()
{
    freopen("fractii.in","r",stdin);
    freopen ("fractii.out","w",stdout);
    int n,i,s=1;
    scanf("%d",&n);
    ciur(n);
    for (i=1;i<=n;i++)
    {
        s=s+2*v[i];
    }
    printf("%d",s);
    return 0;
}