#include<iostream>
#include<algorithm>
#include<string>
#include<vector>
using namespace std;
vector<string> a;
int main()
{
    std::ios::sync_with_stdio(0);
	int n,c,AKIOI,pep=0;
	cin>>n;
	string s[n+1],name[n+1],da[n+1],AC,AK,IOI,ACM,arrive="",start="";
	for(c=1;c<=n;c++)
	{
		cin>>s[c];
		if(s[c]=="start")
		{
			if(a.size()==0)
				da[c]="Error";
			else{
				if(arrive!="")
				a.push_back(arrive);
				if(start!="")
				a.push_back(start);
				if(a.size()==1)
				{
					arrive=a.front();
					da[c]=a.front();
					a.erase(a.begin());
				}
				else{
					arrive=a.front();
					da[c]=a.front();
					da[c]+=" ";
					a.erase(a.begin());
					start=a.front();
					da[c]+=a.front();
					a.erase(a.begin());
				}
			}
		}
		else{
			cin>>name[c];
			if(s[c]=="arrive")
			{
				if(a.size()==0)
				{
					a.push_back(name[c]);
					da[c]="OK";
				}
				else{
					string num_to_find=name[c];
					vector<string>::iterator d=std::find(a.begin(),a.end(),num_to_find);
					if(d!=a.end()||start==name[c]||arrive==name[c])
					da[c]="Error";
					if(da[c]!="Error")
					{
						da[c]="OK";
						a.push_back(name[c]);
					}
				}
			}
			else{
				string num_to_find=name[c];
					vector<string>::iterator d=std::find(a.begin(),a.end(),num_to_find);
					if(d==a.end())
					da[c]="Error";
					if(da[c]!="Error")
					{
						da[c]="OK";
						a.erase(d);
					}
			}
		}
	}
	for(AKIOI=1;AKIOI<=n;AKIOI++)
	cout<<da[AKIOI]<<endl;
	return 0;
}