/* name: 6608
 * author: 5ab
 * created at: 2023-08-26
 */
#include <iostream>
#include <map>
using namespace std;

#define all(x) (x).begin(), (x).end()
#define ssz(x) (int((x).size()))

auto chmax = [](auto& x, auto y) { if (x < y) x = y; };
auto chmin = [](auto& x, auto y) { if (x > y) x = y; };

using ll = long long;
const int max_n = 5e5, max_q = 5e5, max_lgn = 19;

struct node
{
	int l, r, fa;
}
tr[max_n * 2 + max_q * 2 * (max_lgn + 1)];
int rt[max_q + 1], mx[1 << (max_lgn + 1)], ind = 0;
map<int, int> cvl;

int nnode()
{
	tr[ind].l = tr[ind].r = -1;
	return ind++;
}

int build(int l, int r, int fa, int pid)
{
	int id = nnode();
	mx[pid] = id;
	tr[id].fa = fa;
	if (l < r)
	{
		int mid = (l + r) >> 1;
		tr[id].l = build(l, mid, id, pid * 2);
		tr[id].r = build(mid + 1, r, id, pid * 2 + 1);
	}
	return id;
}

void split(int L, int R, int l, int r, int id, int &x, int &y)
{
	if (L <= l && r <= R)
	{
		y = x, x = -1;
		return;
	}
	if (x == -1)
	{
		y = -1;
		return;
	}
	int mid = (l + r) >> 1, lx = -1, rx = -1;
	if (L <= mid)
		split(L, R, l, mid, id * 2, tr[x].l, lx);
	if (mid < R)
		split(L, R, mid + 1, r, id * 2 + 1, tr[x].r, rx);
	
	if (lx == -1 && rx == -1)
	{
		y = -1;
		return;
	}
	if (tr[x].l == -1 && tr[x].r == -1)
	{
		tr[x].l = lx, tr[x].r = rx;
		y = x, x = -1;
	}
	else
	{
		y = nnode();
		tr[y].l = lx, tr[y].r = rx;
		if (lx != -1) tr[lx].fa = y;
		if (rx != -1) tr[rx].fa = y;
		if (mx[id] == x)
			mx[id] = y;
	}
}

void merge(int &x, int y, int fa, int id)
{
	if (x == -1 || y == -1)
	{
		x = x + y + 1;
		if (x != -1)
			tr[x].fa = fa;
		return;
	}
	merge(tr[x].l, tr[y].l, x, id * 2);
	merge(tr[x].r, tr[y].r, x, id * 2 + 1);
	if (mx[id] == y)
		mx[id] = x;
}

int query(int L, int R, int l, int r, int id)
{
	if (L <= l && r <= R)
	{
		int x = mx[id];
		while (tr[x].fa != -1)
			x = tr[x].fa;
		return cvl[x];
	}
	int mid = (l + r) >> 1, ret = 0;
	if (L <= mid)
		chmax(ret, query(L, R, l, mid, id * 2));
	if (mid < R)
		chmax(ret, query(L, R, mid + 1, r, id * 2 + 1));
	return ret;
}

signed main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	
	int n, q;
	
	cin >> n >> q;
	cvl[rt[0] = build(0, n - 1, -1, 1)] = 0;
	
	fill(rt + 1, rt + q + 1, -1);
	
	int opt, l, r, x;
	while (q--)
	{
		cin >> opt >> l >> r, l--, r--;
		if (opt == 1)
		{
			cin >> x;
			int tmp = -1;
			split(l, r, 0, n - 1, 1, rt[x], tmp);
			merge(rt[x + 1], tmp, -1, 1);
			cvl[rt[x]] = x, cvl[rt[x + 1]] = x + 1;
		}
		else
			cout << query(l, r, 0, n - 1, 1) << "\n";
	}
	
	return 0;
}
// started coding at: 08-26 20:21:51