#include<stdio.h>
int v[1000010];
long long N,S;
int main()
{
freopen("fractii.in","r",stdin);
freopen("fractii.out","w",stdout);
scanf("%lld",&N);
for(int i=2;i<=N;++i)
{
        if(v[i]==0)
        {
        v[i]=i-1;
        
        for(int j=i*2;j<=N;j=j+i)
        {       
                if(v[j]==0)
                v[j]=j-(j/i);
                else
                v[j]=v[j]-(v[j]/i);
        }
        }
}
S=1;
for(int i=2;i<=N;++i)
        {
        S=S+v[i]*2;
        }
        printf("%lld",S);
   
return 0;
}