#include<iostream>
#include<queue>
#include<vector>

using namespace std;

deque <int> num;
vector <int> error;

int main() {
	
	int a;
	scanf("%d",&a);
	
	for(int i = 0; i < a; ++i) {
		
		string r;
		cin >> r;
		
		if(r == "LIN") {
			
			int e;
			scanf("%d",&e);
			
			num.push_front(e);
		}
		
		else if(r == "RIN") {
			
			int e;
			scanf("%d",&e);
			
			num.push_back(e);
		}
		
		
		else if(r == "LOUT") {
			
			if(num.empty() == true) {
			
				error.push_back(i);
			}
			
			else {
				
				num.pop_front();
			}
		}
		
		else {
			
			if(num.empty() == true) {
			
				error.push_back(i);
			}
			
			else {
				
				num.pop_back();
			}
		}
	}
	
	for(int i = 0; i < num.size(); ++i) {
		
		printf("%d ",num.front());
		num.pop_front();
	}
	
	printf("\n");
	
	for(int i = 0; i < error.size(); ++i) {
		
		printf("%d ERROR\n",error[i] + 1);
	}
	
	return 0;
}