#include <algorithm>

#include <bitset>

#include <cctype>

#include <cerrno>

#include <clocale>

#include <cmath>

#include <complex>

#include <cstdio>

#include <cstdlib>

#include <cstring>

#include <ctime>

#include <deque>

#include <exception>

#include <fstream>

#include <functional>

#include <limits>

#include <list>

#include <map>

#include <iomanip>

#include <ios>

#include <iosfwd>

#include <iostream>

#include <istream>

#include <ostream>

#include <queue>

#include <set>

#include <sstream>

#include <stdexcept>

#include <streambuf>

#include <string>

#include <utility>

#include <vector>

#include <cwchar>

#include <cwctype>

#include <stack>

#include <limits.h>

using namespace std;

#define MAXN 40010

int i,n,TC,T;

int sum[MAXN];

inline void init()

{

        int i,j,tmp,cnt = ;

        static int f[MAXN],prime[MAXN],phi[MAXN];

        for (i = ; i < MAXN; i++)

        {

                if (!f[i])

                {

                        f[i] = prime[++cnt] = i;

                        phi[i] = i - ;

                }

                for (j = ; j <= cnt; j++)

                {

                        tmp = i * prime[j];

                        if (tmp >= MAXN) break;

                        f[tmp] = prime[j];

                        if (prime[j] == f[i])

                        {

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

                                break;

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

                }

        }

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

}

int main()

{

        init();

        scanf("%d",&n);

        printf("%d\n",*sum[n-]+);

        return ;

}