#include <cstdio>
using namespace std;
char prim[1000000];
void ciur(int n){
    int i,j;
    int multiplii;
    unsigned long long nr=2*n-1;
    for (i=2;i<=n;i++)
    prim[i]=1;
    for (i=2;i<=n;i++){
        if (prim[i]){
            multiplii=0;
            for (j=i+i;j<=n;j=j+i){
                multiplii++;
                prim[j]=0;}
                if (multiplii){
                    nr=nr+(n-multiplii);}                    else {
                        nr=nr+(n-1);
                    }
        }
    }
    printf ("%lld", nr-2);
}
int main()
{
freopen ("fractii.in", "r", stdin);
freopen ("fractii.out", "w", stdout);
int n,i;
scanf ("%d", &n);
if (n==1){
    printf ("%d", 1);}
    if (n==2){
        printf ("%d", 3);}
        else if (n!=1&&n!=2){
ciur(n);}
return 0;
}