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#include <iostream>
#include <fstream>

using namespace std;

bool np[1000000];

int main()
{
    int n,i,j;
    ifstream fin ("fractii.in");
    fin >>n;
    fin.close();
    for (i=2;i<=n/2;i++)
        if(np[i]==0)
            for(j=2*i;j<=n;j+=i)
                np[j]=1;
    
    long long int s=1;
    int fi;
    for (i=2;i<=n;i++)
    {
        if (np[i]==0)
            s+=2*(i-1);
        else
            {    
                fi=i;
                if(i%2==0)
                    fi/=2;
                for (j=3;j<i;j+=2)
                if (np[j]==0 and i%j==0)
                {
                    //cout <<i <<" " <<j <<"\n";
                    fi/=j;
                    fi*=(j-1);
                }
                s+=2*fi;
            }
            //cout <<i <<" " <<s <<"\n";
        }
    ofstream fout ("fracti.out");
    fout <<s;
    fout.close();
    return 0;
}