#include<cstdio>
using namespace std;
long long s=1;
int v[1000005];
void ciur(int x)
{
    for(int i=2;i<=x;++i)
    {
    if(v[i]==0)
    {
        for(int j=2*i;j<=x;j=j+i)
        {
            if(v[j]==0)
                v[j]=(j/i)*(i-1);
            else
                v[j]=(v[j]/i)*(i-1);
        }
        v[i]=i-1;
    }
    s+=(1LL*2*v[i]);
    }
    printf("%lld",s);
}

int main()
{
    freopen("fractii.in","r",stdin);
    freopen("fractii.out","w",stdout);
    int n;
    scanf("%d",&n);
    ciur(n);
    return 0;
}