#include<iostream>
using namespace std;
typedef long long LL;
const int N=1e6+10;
int primes[N],cnt;
int phi[N];
bool st[N];


LL getoula(int n)
{   
    phi[1]=1;
    for(int i=2;i<=n;i++)
    {
        if(!st[i]){
            primes[cnt++]=i;
            phi[i]=i-1;
        }
        for(int j=0;primes[j]<=n/i;j++)
        {
            st[primes[j]*i]=true;
            if(i%primes[j]==0)
            {
                phi[primes[j]*i]=primes[j]*phi[i];
                break;
            }
            if(i%primes[j]!=0)
            {
                phi[primes[j]*i]=(primes[j]-1)*phi[i];

            }

        }
    }
    LL res=0;
    for(int i=1;i<=n;i++)
    {
        res+=phi[i];
    }
    return res;
}


int main()
{

    int n;
    cin>>n;
    cout<<getoula(n)<<endl;


    return 0;
}