#include <bits/stdc++.h>

using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");

int n;

const int nmax = 1e6 + 1;
bitset<nmax> prime;
int a[nmax];
int main()
{
    fin >> n;

    int i , j;
    long long result = 0;

    for(i=1;i<=n;++i)
        a[i] = i;
    for(i=4;i<=n;i+=2 )
        {prime[i] = 1;
         a[i]/= 2;
        }


    for(i=3;i<=n;i+=2)
        if(prime[i] == 0)
    { a[i] = i-1;
        for(j=2*i;j<=n;j+=i)
            {prime[j] = 1;
             a[j] /= i;
             a[j] *= (i-1);
            }

    }
    for(i=3;i<=n;++i)
    {result += 2LL*a[i];
    //fout << a[i] << "\n";
    }

    fout << result + 1 + 2;
    return 0;
}