#include <stdio.h>
#include <cstring>
#include <stdlib.h>
#include <time.h>
#include <bitset>
#include <string>
#include <vector>
#include <math.h>
#include <stack>
#include <queue>
#include <list>
#include <set>
#include <map>
#include <limits.h>
#include <algorithm>
#include <deque>
#define inf 0x3f3f3f3f
#define nmax 1000010
#define eps 1e-12
using namespace std;
int n,i,j;
long long sol,t[nmax];
int main() {
freopen("fractii.in","r",stdin);
freopen("fractii.out","w",stdout);
scanf("%d",&n);
for (i=1;i<=n;i++) t[i]=i;
for (i=2;i<=n;i++)
   if (t[i]==i) {
    for (j=i;j<=n;j+=i) t[j]=t[j]/i,t[j]=t[j]*(i-1);
}
sol=1;
for (i=2;i<=n;i++) sol=sol+t[i]*2;
cout<<sol;
return 0;
}