#include <stdio.h>
int n;
int run()
{
	int i,a[12222],l=0;
	char c;
	while(n>0)
	{
		n--;
		c=' ';
		while((c!='P')&&(c!='O')&&(c!='A'))
			scanf("%c",&c);
		if(c=='P')
		{
			scanf("%d",&i);
			l++;
			a[l]=i;
		}
		if(c=='O')
			if(l>0)
				l--;
		if(c=='A')
		{
			if(l>0)
				printf("%d\n",a[l]);
			else
				printf("E\n");
		}
	}
	printf("\n");
}
int main()
{
	scanf("%d",&n);
	while(n!=0)
	{
		run();
		n=0;
		scanf("%d",&n);
	}
	return 0;
}
/**************************************************************
	Problem: 2192
	User: admin
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:1144 kb
****************************************************************/