C++ :

#include <bits/stdc++.h>
using namespace std;

vector<int> a[100010];//向量数组，相当于二维数组
 
int main(){
	int n,x,y,i;
	string order;//指令
	cin>>n;
	for(i = 1;i <= n;i++){
		cin>>order;//读入指令
		if(order == "ADD"){
			cin>>x>>y;//对第几个问题评论了
			a[x].push_back(y); 
		} else if(order == "QUERY"){
			cin>>x>>y;
			if(a[x].size() < y){
				cout<<"-1"<<endl;
			} else{
				cout<<a[x][y-1]<<endl;
			}
		} 
	}
}