#include <bits/stdc++.h>
#define endl '\n'

using namespace std;
const int MAXN = (int)1e7 + 42;
const int64_t mod = (int64_t)1e9 + 7;

template <class T>
struct fenwick
{
	int sz;
	T tr[MAXN];

	void init(int n)
	{
		sz = n + 1;
		memset(tr, 0, sizeof(tr));
	}

	T query(int idx)
	{
		T ans = 0;
		for(; idx >= 1; idx -= (idx & -idx))
			ans += tr[idx];
		return ans;
	}

	void update(int idx, T val)
	{
		if(idx <= 0) return;
		for(; idx <= sz; idx += (idx & -idx))
			tr[idx] += val;
	}

	T query(int l, int r) { return query(r) - query(l - 1); }
};


int n;

void read()
{
	cin >> n;
}

int64_t answer = 0;
int64_t cnt[MAXN], c[MAXN];
int lp[MAXN];

int64_t C(int64_t x) { return x * 1ll * (x - 1) / 2ll; }

fenwick<int64_t> t;

void solve()
{
	t.init(n);
	for(int i = 2; i <= n; i++)
		if(lp[i] == 0) for(int x = i; x <= n; x += i)
			if(lp[x] == 0) lp[x] = i;

	for(int i = 2; i <= n; i++)
		cnt[i] += (n - i) / i + 1, c[i] += (n - i) / i + 1;

	for(int i = 2; i <= n; i++)
		cnt[i] = C(cnt[i]);
	
	for(int i = n; i >= 1; i--)
		for(int x = i * 2; x <= n; x += i)
			cnt[i] -= cnt[x];

	for(int i = 2; i <= n; i++)
		answer -= cnt[i];

	for(int i = 2; i <= n; i++)
		t.update(lp[i], 1);

	for(int i = 2; i <= n; i++)
	{
		t.update(lp[i], -1);
		int64_t cnt2 = t.query(n / lp[i]);
		int64_t cnt3 = t.query(n / 2);

		cnt3 -= cnt2;
		answer += cnt2 * 2ll;
		if(lp[i] * 2 <= n) answer += cnt3 * 3ll;
	}

	cout << answer << endl;
}

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);

	read();
	solve();
	return 0;
}