#include<cstdio>

#include<cstring>

#include<vector>

#include<iostream>

#include<algorithm>

https://vjudge.net/problem/CodeForces-449Cusing namespace std;

typedef long long ll;

const int N=1e5+;

int su[N];

bool he[N];

void Eratosthenes(int n){

    for(int i=;i<=n;i++){

    if(he[i]!=)continue;

    for(int j=;j*i<=n;j++)he[j*i]=;

    }

    return;

}

vector<int>a;

int p[N][];

bool ok[N];

int main(){

    int n;

    scanf("%d",&n);

    Eratosthenes(n);

    int ans=;

    for(int i=n/;i>=;i--){

    if(he[i])continue;

    a.clear();

    for(int j=i;j<=n;j+=i){

        if(!ok[j]){

        a.push_back(j);

        }

    }

    if(a.size()%)swap(a[],a[a.size()-]);

    for(int j=;j<a.size()-;j+=){

        ans++;

        p[ans][]=a[j];ok[a[j]]=;

        p[ans][]=a[j+];ok[a[j+]]=;

    }

    }

    printf("%d\n",ans);

    for(int i=;i<=ans;i++){

    printf("%d %d\n",p[i][],p[i][]);

    }

    return ;

}