#include <iostream>
using namespace std;
ifstream in("fractii.in");
ofstream out("fractii.out");
int f[1000006];
int main(){
    int n,i,j;
    long long s=0;
    in>>n;
    for(i=2; i<=n; ++i){
        if(!f[i]){
            for(j=i; j<=n; j+=i){
                f[j]+=j/i-1;
            }
        }
        s+=2LL*(i-f[i]-1);
    }
    out<<s;
    return 0;
}