#include<bits/stdc++.h>
using namespace std;

bool zs(long long x)
{
    long long i;
    for(i=2;i<=sqrt(x);i++)
    {
        if(x%i==0)
        {
            return false;
        }
    }
    return true;
}
int main()
{
    freopen("gcd_prime.in","r",stdin);
    freopen("gcd_prime.out","w",stdout);
    long long n,ans,i,j;
    cin>>n;
    ans=0;
    for(i=2;i<=n;i++)
    {
        if(zs(i)==true)
        {
            ans=ans+(n/i)*2-1;
        }
    }
    cout<<ans;
    return 0;
}