/******************************************************************************

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*******************************************************************************/

#include <fstream>
using namespace std;
ifstream f("fractii.in");
ofstream g("fractii.out");
long long n,eu[1000005];
long long solve(long long n)
{
    long long s=0;
    for(int i=1;i<=n;++i) eu[i]=i;
    for(int i=2;i<=n;++i)
        if(eu[i]==i)
        {
            eu[i]--;
            for(int j=i+i;j<=n;j+=i) eu[j]=eu[j]/i*(i-1);
        }
    for(int i=2;i<=n;++i)
        s+=eu[i];
    return s*2+1;
}
int main()
{
    f>>n;
    g<<solve(n)<<'\n';
    return 0;
}