#include <iostream>
#include <cstdio>
using namespace std;


long n,i,j,v[1000005];
long long s;
int main()
{
    freopen("fractii.in","r",stdin);
    freopen("fractii.out","w",stdout);

    scanf("%ld",&n);


    for (i=2;i<=n;i++)
    {
        if (v[i]==0)
        {
            v[i]=i-1;
            for (j=i*2;j<=n;j+=i)
            {
                if (v[j]==0)
                    v[j]=j/i*(i-1);
                else
                    v[j]=v[j]/i*(i-1);
            }
        }
        s+=v[i]*2;
    }

    printf("%lld",s+1);
    return 0;
}