#include <stdio.h>
#include <stdlib.h>
int e[1000000];
void calcul(int n){
    int j,i;

    for(i=2;i<=n;i++)
        e[i]=i;
    for(i=2;i<=n;i++)
        if(e[i]==i)
            for(j=i;j<=n;j+=i)
                e[j]=e[j]/i*(i-1);
}
int main()
{
    freopen("fractii.in","r",stdin);
    freopen("fractii.out","w",stdout);
    int n,i;
    long long s=1;
    scanf("%d",&n);
    calcul(n);
    for(i=2;i<=n;i++)
        s+=2*e[i];
    printf("%lld",s);
    return 0;
}