#include<stdio.h>
FILE *fin,*fout;
int e[1000001],a,nr,i,j;
long long s;
int main()
{
    fin=fopen("fractii.in","r");
    fout=fopen("fractii.out","w");
    fscanf(fin,"%d",&nr);
    for(i=2;i<=nr;i++)
        e[i]=i;
    for(i=2;i<=nr;i++)
    {
        if(e[i]==i)
        {
            for(j=i;j<=nr;j+=i)
                e[j]=e[j]/i*(i-1);
        }
    }
    s=1;
    for(i=2;i<=nr;i++)
    s=s+e[i]*2;
    fprintf(fout,"%lld",s);
    fclose(fin);
    fclose(fout);
    return 0;
}