#include<bits/stdc++.h>

#define maxn 10000005

#define len 100005

#define mod 1000000007

using namespace std;

typedef long long ll;

ll mark[maxn];

ll phi[maxn];

ll pri[maxn];

ll sum[maxn];

int tot;

ll n;

void getphi()//欧拉表

{

    phi[]=;

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

    {

        if(!mark[i]){phi[i]=i-;pri[++tot]=i;}

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

        {

            int x=pri[j];

            if(i*x>n)break;

            mark[i*x]=;

            if(i%x==){phi[i*x]=phi[i]*x;break;}

            else phi[i*x]=phi[i]*phi[x];

        }

    }

}

int main(){

    scanf("%lld",&n);

    getphi();

    sum[]=phi[];

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

    ll num=;

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

        num+=*sum[n/pri[i]]-;

    }

    printf("%lld",num);

}