#include <bits/stdc++.h>
using namespace std;

typedef long long LL;
const int N=1e6+5;

int PRIMES[N];
bool vis[N];
int PHI[N];
int n;

// 使用线性筛法计算Euler Function
LL getEulerFunc(){
    int cnt=0;
    PHI[1]=1; //1的Euler Function进行特殊处理
    for(int i=2; i<=n; ++i){
        if(!vis[i]) {PRIMES[cnt++]=i; PHI[i]=i-1;}
        for(int j=0; PRIMES[j]<=n/i; ++j){
            vis[PRIMES[j]*i]=true;
            if(i%PRIMES[j]==0){
                PHI[PRIMES[j]*i]=PHI[i]*PRIMES[j];
                break;
            }
            else 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(){
    memset(PRIMES, 0X00, sizeof PRIMES);
    memset(vis, 0x00, sizeof vis);
    memset(PHI, 0x00, sizeof PHI);
    cin>>n;
    cout<<getEulerFunc()<<endl;

    return 0;
}