C++ :

#include<bits/stdc++.h>
using namespace std;
int n,c;
string s[1000005],t;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>t;
		bool f=0;
		int tt;
		for(int j=1;j<=c;j++){
			if(t==s[j]){
				f=1;
				tt=j;
				break;
			}
		}
		if(f==0){
			c++;
			s[c]=t;
		}
		else{
			c++;
			s[c]=t;
			s[tt]=" ";
		}
	}
	bool ff=0;
	for(int i=1;i<=c;i++){
		if(s[i]!=" "){
			if(ff==0&&s[i]=="y"){
				cout<<"y\nz\nx";
				return 0;
			}
			else cout<<s[i]<<"\n";
			ff=1;
		}
	}
	return 0;
}

Python :

# coding=utf-8
n=int(input())
lst=[]
dic={}
for i in range(n):
    a=input()
    if(a not in dic):
        dic[a]=1
    else :
        dic[a]+=1
    if(dic[a]==1):
        lst.append(a)
    elif(dic[a]==2):
        lst.remove(a)
        lst.append(a)
for i in lst:
    print(i)