#include<bits/stdc++.h>

#define LL long long

#define fi first

#define se second

#define mk make_pair

#define PLL pair<LL, LL>

#define PLI pair<LL, int>

#define PII pair<int, int>

#define SZ(x) ((int)x.size())

#define ull unsigned long long

using namespace std;

const int N = 1e5 + ;

const int inf = 0x3f3f3f3f;

const LL INF = 0x3f3f3f3f3f3f3f3f;

const int mod = 1e9 + ;

const double eps = 1e-;

const double PI = acos(-);

int n;

bool vis[N];

bool prime[N];

queue<int> que;

vector<PII> ans;

int main() {

    memset(prime, true, sizeof(prime));

    prime[] = prime[] = false;

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

        if(!prime[i]) continue;

        for(int j = i * ; j < N; j += i)

            prime[j] = false;

    }

    scanf("%d", &n);

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

        if(!prime[i]) continue;

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

            if(!vis[j]) que.push(j);

        que.push(i);

        if( * i <= n && !vis[ * i]) que.push( * i);

        while(SZ(que) >= ) {

            int x = que.front(); que.pop();

            int y = que.front(); que.pop();

            vis[x] = vis[y] = true;

            ans.push_back(mk(x, y));

        }

        while(SZ(que)) que.pop();

    }

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

    for(auto& t : ans) printf("%d %d\n", t.fi, t.se);

    puts("");

    return ;

}

/*

*/