#include <iostream>

#include <cstdio>

#include <cstdlib>

#include <cstring>

#include <algorithm>

#include <vector>

#include <queue>

inline void read(long long &x){x = ;char ch = getchar();char c = ch;while(ch > '' || ch < '')c = ch, ch = getchar();while(ch >= '' && ch <= '')x = x *  + ch - '', ch = getchar();}

inline int max(int a, int b){return a > b ? a : b;}

inline int min(int a, int b){return a < b ? a : b;}

inline void swap(int &a, int &b){int tmp = a;a = b;b = tmp;}

const int INF = 0x3f3f3f3f;

const int MAXN =  + ;

long long n;

long long ans;

long long prime[MAXN],phi[MAXN],cnt;

bool bp[MAXN];

inline void makephi()

{

    phi[] = ;

    for(register long long i = ;i <= n;++ i)

    {

        if(!bp[i])

            prime[++cnt] = i, phi[i] = i - ;

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

        {

            if(i * prime[j] > n)break;

            bp[i* prime[j]] = ;

            if(i % prime[j] == )

            {

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

                break;

            }

            else

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

        }

    }

}

long long f[MAXN];

int main()

{

    read(n);

    makephi();

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

    {

        for(register int j = i * ;j <= n;j += i)

        {

            f[j] += phi[j / i] * i;

        }

    }

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

        ans += f[i];

    printf("%lld", ans);

    return ;

}