#include <bits/stdc++.h>
#define N 500007

using namespace std;

int n, q, tot, rt[N], lc[N * 50], rc[N * 50];

void build(int &u, int l, int r) {
    u = ++tot;
    if (l == r)
        return;
    int mid = l + r >> 1;
    build(lc[u], l, mid), build(rc[u], mid + 1, r);
}

void update(int u, int &v, int l, int r, int L, int R) {
    if (!u)
        return;
    if (l >= L && r <= R)
        return v = u, void();
    if (!v)
        v = ++tot;
    int mid = l + r >> 1;
    if (L <= mid)
        update(lc[u], lc[v], l, mid, L, R);
    if (R > mid)
        update(rc[u], rc[v], mid + 1, r, L, R);
    if (!lc[v] && !rc[v])
        v = 0;
}

int query(int u, int l, int r, int L, int R) {
    if (!u)
        return 0;
    if (l >= L && r <= R)
        return 1;
    int mid = l + r >> 1, ret = 0;
    if (L <= mid)
        ret |= query(lc[u], l, mid, L, R);
    if (R > mid)
        ret |= query(rc[u], mid + 1, r, L, R);
    return ret;
}

int main() {
    scanf("%d%d", &n, &q);
    build(rt[0], 1, n);
    for (int i = 1; i <= q; i++) {
        int opt, l, r, x;
        scanf("%d", &opt);
        if (opt == 1) {
            scanf("%d%d%d", &l, &r, &x);
            update(rt[x], rt[x + 1], 1, n, l, r);
        } else {
            scanf("%d%d", &l, &r);
            int L = 1, R = i;
            while (L <= R) {
                int mid = L + R >> 1;
                if (query(rt[mid], 1, n, l, r))
                    L = mid + 1;
                else
                    R = mid - 1;
            }
            printf("%d\n", R);
        }
    }
    return 0;
}