#include<iostream>

#include<cstdio>

#include<cstring>

using namespace std;

int n;

int ans=;

int phi[];

int vis[]={};

int prime[],cntprime=;

int Lineshake(){

    vis[]=;phi[]=;

    for(int i=;i<=n;++i){

        if(!vis[i]){

            prime[++cntprime]=i;

            phi[i]=i-;

        }

        for(int j=;(j<=cntprime)&&(i*prime[j]<=n);++j){

            vis[i*prime[j]]=;

            if(i%prime[j]==){

                phi[i*prime[j]]=phi[i]*prime[j];

                break;

            }

            phi[i*prime[j]]=phi[i]*(prime[j]-);

        }

    }

}

int main(){

    scanf("%d",&n);

    Lineshake();

    for(int i=;i<=n-;++i)ans=ans+phi[i]*;

    printf("%d\n",ans+);

    return ;

}