#include<fstream>
#include<set>
#include<algorithm>
#include<cstring>
using namespace std;
ifstream fin("zeap.in");
ofstream fout("zeap.out");
set<int> v;
char x[20];
int n;
int minim=(1<<30),code;
char *p;
void min_find()
{
	minim=(1<<30);
	if(v.size()<2)
		return;
	set<int>::iterator it1,it2;
	it1=v.begin();
	it2=it1++;
	for(;it1!=v.end();it1++,it2++)
		minim=min(minim,(*it1)-(*it2));
}
void decode()
{
	if(x[0]=='M')
	{
		code=4;
		return;
	}
	if(x[0]=='I')
		code=1;
	if(x[0]=='S')
		code=2;
	if(x[0]=='C')
		code=3;
	p=strchr(x,' ');
	n=atoi(p+1);
}
int main()
{
	while(fin.getline(x,20))
	{
		decode();
		if(v.size()==2)
			min_find();
		if(code==1)
		{
			pair<set<int>::iterator,bool> is;
			set<int>::iterator it1,it2,it3;
			is=v.insert(n);
			if(is.second && v.size()>2)
			{
				it3=is.first;
				int d1=(1<<30),d2=(1<<30);
				if(it3==v.begin())
				{
					it2=it3++;
					d2=(*it3)-(*it2);
					minim=min(minim,d2);
					continue;
				}
				it2=it3++;
				it1=--it2;
				it2++;
				if(it3==v.end())
				{
					d1=(*it2)-(*it1);
					minim=min(minim,d1);
					continue;
				}
				d1=(*it2)-(*it1);
				d2=(*it3)-(*it2);
				minim=min(minim,min(d1,d2));
			}
			continue;
		}
		if(code==2)
		{
			if(!v.erase(n))
				fout<<-1<<'\n';
			else
				min_find();
			continue;
		}
		if(code==3)
		{
			fout<<(v.find(n)!=v.end())<<'\n';
			continue;
		}
		/*if(code==4)
		{
			if(v.size()<2)
			{
				fout<<-1<<'\n';
				continue;
			}
			set<int>::iterator it1,it2;
			if(x[1]=='A')
			{
				it1=v.end();
				it1--;
				it2=v.begin();
				fout<<(*it1)-(*it2)<<'\n';
			}
			else
				fout<<minim<<'\n';
		}*/
	}
	fin.close();
	fout.close();
	return 0;
}