#include <bits/stdc++.h>
#define LL long long
#define ULL unsigned long long
#define pii pair<int, int>
#define fi first
#define se second
#define mkp make_pair
#define sz(x) (int)x.size()
using namespace std;
bool Mst;

LL read() {
	LL s = 0, f = 1;
	char ch = getchar();
	while (ch < '0' || ch > '9')
		f = (ch == '-' ? -1 : 1), ch = getchar();
	while (ch >= '0' && ch <= '9')
		s = (s << 1) + (s << 3) + (ch ^ 48), ch = getchar();
	return s * f;
}

const int MAXN = 500005;

int n, q;
int a[MAXN];

#define mid ((l + r) >> 1)

int ls[MAXN << 5], rs[MAXN << 5], rt[MAXN], tot = 0, sum[MAXN << 5];

void build(int l, int r, int &p) {
	p = ++tot, sum[p] = 1;
	if (l == r) return ;
	build(l, mid, ls[p]), build(mid + 1, r, rs[p]);
}

int copy(int x) {
	int p = ++tot;
	ls[p] = ls[x], rs[p] = rs[x], sum[p] = sum[x];
	return p;
}

int mdf(int l, int r, int p, int q, int x, int y) {
	if (!p) return 0;
	if (x <= l && r <= y) return copy(p);
	int rt = copy(q);
	if (x <= mid) ls[rt] = mdf(l, mid, ls[p], ls[q], x, y);
	if (mid < y) rs[rt] = mdf(mid + 1, r, rs[p], rs[q], x, y);
	sum[rt] = sum[ls[rt]] | sum[rs[rt]];
	return rt;
}

int qry(int l, int r, int p, int x, int y) {
	if (r < x || y < l || !p) return 0;
	if (x <= l && r <= y) return sum[p];
	return qry(l, mid, ls[p], x, y) | qry(mid + 1, r, rs[p], x, y);
}

#undef mid

bool Med;
signed main() {
//	freopen("ex_data.in", "r", stdin);
//	freopen("1.out", "w", stdout);
	n = read(), q = read(), build(1, n, rt[0]);
	while (q--) {
		int op = read(), l = read(), r = read();
		if (op == 1) {
			int x = read();
			rt[x + 1] = mdf(1, n, rt[x], rt[x + 1], l, r);
		}
		else {
			int L = 0, R = 5e5 + 2;
			while (R - L > 1) {
				int mid = (L + R) >> 1;
				if (qry(1, n, rt[mid], l, r)) L = mid;
				else R = mid;
			}
			printf("%d\n", L);
		}
	}
	return 0;
}