#include<stdio.h>  
 #define MAX 1000002  
 int n,F[MAX];  
 void init()  
 {  
     int i,j;  
     for(i=2;i<=n;++i)  
         F[i]=i;  
     for(i=2;i<=n;++i)  
         if(F[i]==i)  
             for(j=i;j<=n;j+=i)  
                 F[j]=F[j]/i*(i-1);  
 }  
 inline long long calcul()  
 {  
     int i;  
     long long sum=1;  
     for(i=2;i<=n;i++)  
         sum+=(F[i]<<1);  
     return sum;  
 }  
 int main()  
 {  
     freopen("fractii.in","r",stdin);  
     freopen("fractii.out","w",stdout);  
     scanf("%d",&n);  
     init();  
     printf("%lld",calcul());  
     return 0;  
 }