#include <cstdio>

using namespace std;

unsigned long long phi[1000005];

int main()
{
    freopen("fractii.in","r",stdin);
    freopen("fractii.out","w",stdout);
    unsigned long long sum=1;
    int n;
    scanf("%d",&n);
    for (int i = 2; i<=n; i++)
        phi[i] = i-1;
    for (int i = 2; i<=n; i++)
    {
        sum+=2*phi[i];
        for (int j = i+i; j<=n; j+=i)
            phi[j]-=phi[i];
    }
    printf("%llu",sum);
}