#include<cstdio>
#define Nmax 1000005
using namespace std;
int n, phi[Nmax], Nrf=1;
int main(){
    freopen("fractii.in", "r", stdin);
    scanf("%d", &n);
    for(int i=1; i<=n; ++i)
        phi[i]=i-1;
    for(int i=2; i<=n; ++i){
     Nrf+=2*phi[i];
        for(int j=2*i; j<=n; j+=i)
            phi[j]-=phi[i];
    }
    freopen("fractii.out", "w", stdout);
    printf("%d\n", Nrf);
return 0;
}