#include<iostream>
#include<cstdio>
using namespace std;

const int N = 1e6+10;
int n, cnt, prime[N], phi[N];
bool sta[N];

void get_ola(int n)
{
    phi[1] = 1;
    for(int i = 2; i <= n; i ++)
    {
        if(sta[i] == false)
        {
            prime[cnt++] = i;//计入质数
            phi[i] = i-1;//质数的欧拉函数
        }

        //对于每个i都要尝试循环
        for(int j = 0; prime[j] <= n/i; j ++)
        {
            sta[prime[j]*i] = true;//先筛去

            if(i % prime[j] == 0)
            {
                phi[prime[j]*i] = phi[i]*prime[j];
                break;
            }
            else
            {
                phi[prime[j]*i] = phi[i]*(prime[j]-1);
            }
        }

    }
}

int main()
{
    scanf("%d", &n);
    get_ola(n);
    long long res = 0;
    for(int i = 1; i <= n; i ++)
        res += phi[i];
    printf("%lld", res);
    return 0;
}