#include<cstdio>
using namespace std;
int e[1000001];
int main(){
    freopen ("fractii.in","r",stdin);
    freopen ("fractii.out","w",stdout);
    int n,i,j;
    long long s=1;
    scanf ("%d",&n);
    for(i=1;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);
        s=s+(e[i]*2);
    }
    printf ("%lld",s);
    return 0;
}