萌新求助，第4个点uke 评测记录

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
void read(int &x){
	char c=getchar();
	int k=1;
	while(c<'0'||c>'9') {if(c=='-') k=-1;c=getchar();}
	for(x=0;c>='0'&&c<='9';c=getchar())
	x=x*10+c-'0';
	x*=k;
}
int n,k,m,a[200001],x;
int main(){
	read(m);
	a[0]=0;
	while(m--){
		read(k);
		switch(k){
			case 0:read(x);n++;a[n]=max(a[n-1],x);break;
			case 1:if(n!=0) n--;break;
			case 2:printf("%d\n",a[n]);
		}
	}
	return 0;
}

我太菜了，路过的巨佬帮忙