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#include <iostream>
#include<fstream>
#include<vector>
#include<math.h>

using namespace std;
int main()
{
    long long n;
    int * v = new int[1000001];
    int * nrPrime= new int[1000001];
    int * nrPrimeIndex = new int [1000001];
    int * altVector = new int [1000001];
    int count=0;
    long long numere=0;
    ifstream f("fractii.in");
    ofstream g("fractii.out");
    f>>n;
    for(long long i=2;i<=n;i++)
    {
        if(v[i]==0)
        {
            nrPrime[i]=1;
            nrPrimeIndex[count]=i;
            count++;
            v[i]=1;
        }
        for(long long j=i*i;j<=n;j+=i)
        {
            v[j]=1;
        }
    }
    for(int index=2;index<=n;index++)
    {
        if(nrPrime[index]==1)
        {
            numere=numere+(index-1);
        }
        else
        {
            int copie=index;
            int i=0;
            int k=0;
            while(copie>1)
            {
                if(copie%nrPrimeIndex[i]==0)
                while(copie%nrPrimeIndex[i]==0)
                {
                    altVector[nrPrimeIndex[i]]++;
                    copie=copie/nrPrimeIndex[i];
                }
                i++;
            }
            long long produs=1;
            for(int parcurgere=2;parcurgere<=nrPrimeIndex[i];parcurgere++)
            {
                if(altVector[parcurgere]>0)
                {
                    produs=produs*((parcurgere-1)*(pow(parcurgere,altVector[parcurgere]-1)));
                    altVector[parcurgere]=0;
                }
            }
            numere=numere+produs;
        }
    }
    numere=numere*2+1;
    g<<numere;
    f.close();
    g.close();
    return 0;
}