#include <iostream>
#include <unordered_map>
using namespace std;

typedef struct NODE*node;
typedef long long ll;
struct NODE
{
	int value;
	node next;
};

node getNODE(int data)
{
	node p = new NODE;
	if (p == NULL)
		return NULL;
	p->value = data;
	p->next = NULL;
	return p;
}

void AddLast(node &head, node &tail, int data)
{
	node p = getNODE(data);
	if (p == NULL)
	{
		cout << "Loi khong du bo nho!!!" << endl;
		exit(0);
	}
	if (head == NULL)
	{
		head = p;
		tail = p;
	}
	else
	{
		tail->next = p;
		tail = p;
	}
}

void PrintList(node head)
{
	if (head == NULL)
	{
		cout << "Danh sach rong!!!" << endl;
		return;
	}
	node p = head;
	cout << "Danh sach cac phan tu la: " << endl << "\t";
	for (p; p != NULL; p = p->next)
	{
		cout << p->value << "  ";
	}
	cout << endl;
}

void DestroyList(node head)
{
	while (head)
	{
		node p = head;
		head = p->next;
		delete p;
	}
}

int Cau3(node head)
{
	unordered_map<int, int>temp;
	node p = head, q = head;
	for (p; p != NULL; p = p->next)
	{
		temp[p->value]++;
	}
	for (q; q != NULL; q = q->next)
	{
		if (temp[q->value] >= 2)
			return q->value;
	}
	return -1;
}

int main()
{

	node head = NULL, tail = NULL;
	int k;
	cout << "Nhap vao cac so nguyen, nhap mot ki tu bat ki de dung viec nhap" << endl;
	while (cin >> k)
	{
		AddLast(head, tail, k);
	}
	system("cls");
	PrintList(head);
	cout << "Phan tu trung lap dau tien: ";
	cout << Cau3(head) << endl;
	delete head;
	delete tail;
	system("pause");
	return 0;
}