#define N 1000000
#include <iostream>

int c[N + 1] ;

int main()
{
    FILE *fin, *fout;
    fin = fopen("fractii.in", "r");
    fout = fopen("fractii.out", "w");

    int n ;
    long long sum = 1 ;
    fscanf(fin, "%d", &n) ;

    for(int i = 2 ; i <= n ; i++)
        c[i] = i ;

    for(int i = 2 ; i <= n ; i++)
        if(c[i] == i)
            for(int j = i ; j <= n ; j = j + i)
                c[j] = c[j] / i * (i - 1) ;

    for(int i = 2 ; i <= n ; i++)
        sum = sum + c[i] * 2 ;

    fprintf(fout, "%lld", sum) ;

    fclose(fin);
    fclose(fout);
    return 0;
}