#include<bits/stdc++.h>
using namespace std;
const int maxn=5e5+5;
int n,q,cnt;
int ls[maxn*30],rs[maxn*30],rt[maxn],p[maxn*4],w[maxn*30],fa[maxn*30];
int build(int id,int l,int r)
{
	int x=++cnt;
	p[id]=x;
	if(l==r) return x;
	int mid=(l+r)>>1;
	ls[x]=build(id<<1,l,mid);
	rs[x]=build(id<<1|1,mid+1,r);
	fa[ls[x]]=fa[rs[x]]=x;
	return x;
}
int merge(int id1,int id2,int l,int r)
{
	if(id1==0 || id2==0) return id1+id2;
	if(l==r) return id1;
	int mid=(l+r)>>1;
	ls[id1]=merge(ls[id1],ls[id2],l,mid);
	rs[id1]=merge(rs[id1],rs[id2],mid+1,r);
	fa[ls[id1]]=fa[rs[id1]]=id1;
	return id1;
}
int update(int id,int &id1,int &id2,int l,int r,int x,int y)
{
	if(id1==0) return 0;
	if(id2==0) id2=++cnt;
	if(l>=x && r<=y)
	{
		id2=merge(id2,id1,l,r);
		if(p[id]==id1) p[id]=id2;
		id1=0;
		return;
	}
	int mid=(l+r)>>1,ret=0;
	if(x<=mid) ret+=update(id<<1,ls[id1],ls[id2],l,mid,x,y);
	if(y>mid) ret+=update(id<<1|1,rs[id1],rs[id2],mid+1,r,x,y);
	fa[ls[id1]]=fa[rs[id1]]=id1,fa[ls[id2]]=fa[rs[id2]]=id2;
	if(l!=r && ls[id1]+rs[id1]==0) id1=0;
	if(l!=r && ls[id2]+rs[id2]==0) id2=0;
	if(ret>0) if(p[id]==id1) p[id]=id2;
	return ret;
}
int query(int id,int l,int r,int x,int y)
{
	if(l>=x && r<=y)
	{
		id=p[id];
		while(fa[id]!=0) id=fa[id];
		return w[id];
	}
	int mid=(l+r)>>1,ret=0;
	if(x<=mid) ret=max(ret,query(id<<1,l,mid,x,y));
	if(y>mid) ret=max(ret,query(id<<1|1,mid+1,r,x,y));
	return ret;
}
int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);cout.tie(0);
	int k,l,r,x;
	cin>>n>>q;
	rt[0]=build(1,1,n);
	for(int i=1;i<=q;i++)
	{
		cin>>k>>l>>r;
		if(k==1)
		{
			cin>>x;
			if(x>q) continue;
			w[rt[x]]=w[rt[x+1]]=0;
			update(1,rt[x],rt[x+1],1,n,l,r);
			w[rt[x]]=x,w[rt[x+1]]=x+1;
		}
		if(k==2) cout<<query(1,1,n,l,r)<<'\n';
	}
	return 0;
}

answer.code: In function ‘int update(int, int&, int&, int, int, int, int)’:
answer.code:36:17: error: return-statement with no value, in function returning ‘int’ [-fpermissive]
   36 |                 return;
      |                 ^~~~~~