#include <iostream>

#include <stdio.h>

#include <string.h>

#include <algorithm>

using namespace std;

const int N = 1e7+;

const int INF=0x3f3f3f3f;

typedef unsigned long long ULL;

typedef long long LL;

bool check[N];

int phi[N],prime[N],tot,n;

LL sum[N];

int main(){

    scanf("%d",&n);

    phi[]=;tot=;

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

      if(!check[i]){

        prime[++tot]=i;

        phi[i]=i-;

      }

      for(int j=;j<=tot;++j){

        if(i*prime[j]>n)break;

        check[i*prime[j]]=true;

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

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

          break;

        }

        else

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

      }

    }

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

     sum[i]=sum[i-]+phi[i];

    LL ans=;

    for(int i=;i<=tot;++i)

     ans+=*sum[n/prime[i]]-;

    printf("%lld\n",ans);

    return ;

}