// test.cpp: 定义控制台应用程序的入口点。
//
#include "stdafx.h"
#include<iostream>
#include <stdio.h>
#include<sstream>
#include<algorithm>
using namespace std;
void s2i(string &str, int n) {
    stringstream ss;
    ss << str;
    ss >> n;
}
const int MaxN = 10000;
int line;
int inputdata[MaxN];
int main()
{
    cin >> line;
    getchar();//把换行符吃掉
    int index = 0;
    for (int i = 0; i < line; i++) {
        string s;
        getline(cin, s);//读取一行,将读取内容赋给s
        istringstream iss(s);//封装s到iss中
        string tmp;
        while (getline(iss, tmp,' ')) {//getline()自带分割功能但是输入流要是iss
             s2i(tmp,inputdata[index++]);
        }
    }
    //调用algorithm中的sort()函数 传递数组的首尾地址
    sort(inputdata,inputdata+index);
    int a, b;
    for (int i = 1; i > index; i++) {
        if (inputdata[i - 1] == inputdata[i] + 2)a = inputdata[i - 1] + 1;
        if (inputdata[i - 1] == inputdata[i])b = inputdata[i - 1];
        
    }
    cout << a << b << endl;
    return 0;
}