code：

#include<bits/stdc++.h>

#define int long long
#define end '\n'

using namespace std;

inline int read(){
	int x = 0, f = 1;
  char ch = getchar();
	while(ch < '0' || ch > '9'){
    if(ch == '-'){
      f = -1;
    }
    ch = getchar();
  }
	while(ch >= '0' && ch <= '9'){
    x = x * 10 + ch - 48;
    ch = getchar();
  }
	return x * f;
}

const int N = 5e5 + 5;

int n, m;
int a[N];

struct Segment_Tree{
  int mini, maxi, tag1, tag2;
}tree[N * 4];

void pushup(int node){
  tree[node].maxi = max(tree[node << 1].maxi, tree[node << 1 | 1].maxi);
  tree[node].mini = min(tree[node << 1].mini, tree[node << 1 | 1].mini);
}

void addtag1(int node, int val){
  tree[node].maxi += val;
  tree[node].mini += val;
  tree[node].tag1 += val;
}

void addtag2(int node, int val){
  tree[node].maxi = val;
  tree[node].mini = val;
  tree[node].tag2 = val;
  tree[node].tag1 = 0;
}

void pushdown(int node, int lt, int rt){
  if(tree[node].tag2 != 0){
    addtag2(node << 1, tree[node].tag2);
    addtag2(node << 1 | 1, tree[node].tag2);
    tree[node].tag2 = 0;
  }
  if(tree[node].tag1 != 0){
    addtag1(node << 1, tree[node].tag1);
    addtag1(node << 1 | 1, tree[node].tag1);
    tree[node].tag1 = 0;
  }
}

void build(int node, int lt, int rt){
  if(lt == rt){
    tree[node].maxi = tree[node].mini = a[lt];
    return ;
  }
  int mid = lt + rt >> 1;
  build(node << 1, lt, mid);
  build(node << 1 | 1, mid + 1, rt);
  pushup(node);
}

void update(int node, int lt, int rt, int x, int y, int val){
  if(x > rt || y < lt){
    return ;
  }
  if(x <= lt && rt <= y){
    addtag1(node, val);
    return ;
  }
  pushdown(node, lt, rt);
  int mid = lt + rt >> 1;
  update(node << 1, lt, mid, x, y, val);
  update(node << 1 | 1, mid + 1, rt, x, y, val);
  pushup(node);
}

void update_min(int node, int lt, int rt, int x, int y, int val){
  if(x > rt || y < lt){
    return ;
  }
  if(x <= lt && rt <= y){
    if(tree[node].mini >= val){
      tree[node].mini = tree[node].maxi = tree[node].tag2 = val;
      tree[node].tag1 = 0;
    }
    if(tree[node].maxi <= val){
      return ;
    }
    pushdown(node, lt, rt);
    int mid = lt + rt >> 1;
    update_min(node << 1, lt, mid, x, y, val);
    update_min(node << 1 | 1, mid + 1, rt, x, y, val);
    pushup(node);
    return ;
  }
  pushdown(node, lt, rt);
  int mid = lt + rt >> 1;
  update_min(node << 1, lt, mid, x, y, val);
  update_min(node << 1 | 1, mid + 1, rt, x, y, val);
  pushup(node);
}

void update_max(int node, int lt, int rt, int x, int y, int val){
  if(x > rt || y < lt){
    return ;
  }
  if(x <= lt && rt <= y){
    if(tree[node].maxi <= val){
      tree[node].mini = tree[node].maxi = tree[node].tag2 = val;
      tree[node].tag1 = 0;
    }
    if(tree[node].mini >= val){
      return ;
    }
    pushdown(node, lt, rt);
    int mid = lt + rt >> 1;
    update_min(node << 1, lt, mid, x, y, val);
    update_min(node << 1 | 1, mid + 1, rt, x, y, val);
    pushup(node);
    return ;
  }
  pushdown(node, lt, rt);
  int mid = lt + rt >> 1;
  update_min(node << 1, lt, mid, x, y, val);
  update_min(node << 1 | 1, mid + 1, rt, x, y, val);
  pushup(node);
}

int query(int node, int lt, int rt, int x, int y){
  if(x > rt || y < lt){
    return -1e9;
  }
  if(x <= lt && rt <= y){
    return tree[node].maxi;
  }
  pushdown(node, lt, rt);
  int mid = lt + rt >> 1;
  return max(query(node << 1, lt, mid, x, y), query(node << 1 | 1, mid + 1, rt, x, y));
}

void Solve(){
  cin >> n >> m;
  for(int i = 1; i <= n; i++){
    a[i] = read();
  }
  build(1, 1, n);
  while(m--){
    int op;
    cin >> op;
    if(op == 1){
      int x, y, k;
      x = read(), y = read(), k = read();
      update(1, 1, n, x, y, k);
    }
    if(op == 2){
      int x, y, k;
      x = read(), y = read(), k = read();
      update_min(1, 1, n, x, y, k);
    }
    if(op == 3){
      int x, y, k;
      x = read(), y = read(), k = read();
      update_max(1, 1, n, x, y, k);
    }
    if(op == 4){
      int x, y;
      x = read(), y = read();
      printf("%lld\n", query(1, 1, n, x, y));
    }
  }
}

signed main(){
  Solve();
  return 0;
}