#include<stdio.h>          
int n,e[1000001];     
void init()     
{     
    int i,j;     
    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);     
}     
inline long long calcul()     
{     
    int i;     
    long long sum=1;     
    for(i=2;i<=n;i++)     
        sum+=(e[i]*2);     
    return sum;     
}     
int main()     
{     
    freopen("fractii.in","r",stdin);     
    freopen("fractii.out","w",stdout);     
    scanf("%d",&n);     
    init();     
    printf("%lld",calcul());     
    return 0;     
}