//%std
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
inline int read()
{
	int out = 0, fh = 1;
	char jp = getchar();
	while ((jp > '9' || jp < '0') && jp != '-')
		jp = getchar();
	if (jp == '-')
		fh = -1, jp = getchar();
	while (jp >= '0' && jp <= '9')
		out = out * 10 + jp - '0', jp = getchar();
	return out * fh;
}
void print(int x)
{
	if (x >= 10)
		print(x / 10);
	putchar('0' + x % 10);
}
void write(int x, char c)
{
	if (x < 0)
		putchar('-'), x = -x;
	print(x);
	putchar(c);
}
const int N = 1e5 + 10;
int n, vis[N], p[N], cnt, rest[N], tot = 0;
vector<pair<int, int> > ans;
void report(int x, int y)
{
	ans.push_back(make_pair(x, y));
}
int main()
{
	n = read();
	for (int i = 3; i <= n; ++i)
		if (!vis[i] && i % 2)
		{
			if (i * 2 <= n)
			{
				cnt = 0;
				for (int j = i; j <= n; j += i)
					if (!vis[j])
					{
						vis[j] = 1;
						p[++cnt] = j;
					}
				swap(p[2], p[cnt]);				
				for (int k = 2; k <= cnt; k += 2)
					report(p[k - 1], p[k]);
				if (cnt & 1)
					rest[++tot] = p[cnt];
			}
			else
				vis[i] = 1;
		}
	for (int i = 2; i <= n; ++i)
		if (!vis[i])
			rest[++tot] = i;
	for (int k = 2; k <= tot; k += 2)
		report(rest[k - 1], rest[k]);
	cout << ans.size() << '\n';
	for (auto tmp : ans)
		write(tmp.first, ' '), write(tmp.second, '\n');	
	return 0;
}