#include <bits/stdc++.h>

using namespace std;

#define FILE_IO

typedef long long LL;

int n, i, j;
LL ans;
int phi[1000005];

int main()
{
    #ifdef FILE_IO
    freopen("fractii.in", "r", stdin);
    freopen("fractii.out", "w", stdout);
    #endif

    scanf("%d", &n);
    for(i = 1; i <= n; i++)
        phi[i] = i;
    ans = 1;
    for(i = 2; i <= n; i++)
    {
        if(phi[i] == i)
            for(j = i; j <= n; j += i)
                phi[j] = phi[j] / i * (i - 1);
        ans += 2 * phi[i];
    }
    printf("%lld", ans);

    return 0;
}