using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Math;
 
public class Hello{
    public static void Main(){
        int[] num = inta();
        int nummin = 0;
        int nummax = 0;
        if(num[0] == 1){
            nummin = 0;
            nummax = 9;
        }else if(num[0] == 2){
            nummin = 10;
            nummax = 99;
        }else{
            nummin = 100;
            nummax = 999;
        }
        int ans = -2;
        int[,] jd = inta2(num[1],2);
        for(int i=nummin;i<=nummax;i++){
            int count = 0;
            for(int j=0;j<num[1];j++){
                if(jd[j,0] == 3){
                    int check = i%10;

                    if(check != jd[j,1]){
                        ans = -1;
                        break;
                    }
                }else if(jd[j,0] == 2){
                    int check = (i%100)/10;

                    if(check != jd[j,1]){
                        ans = -1;
                        break;
                    }
                }else if(jd[j,0] == 1){
                    int check = i/100;

                    if(check != jd[j,1]){
                        ans = -1;
                        break;
                    }
                }
                count++;
            }

            if(count == num[1]){
                ans = i;
                break;
            }
        }
        for(int i=0;i<num[1];i++){
            for(int j=1;j<num[1];j++){
                if(jd[i,0] == jd[j,0] && jd[i,1] != jd[j,1]){
                    ans = -1;
                }
            }
        }
        WriteLine(ans);

    
    }
    //各種読取
    static string rstr(){ return ReadLine(); }
    static int rint(){ return int.Parse(ReadLine()); }
    static long rlong(){ return long.Parse(ReadLine()); }
    static string[] stra(){ return ReadLine().Split(' '); }
    static int[] inta(){ string[] read_str_array = ReadLine().Split(' '); int[] return_int_array = new int[read_str_array.Length]; for(int countup_i=0;countup_i<read_str_array.Length;countup_i++){ return_int_array[countup_i] = int.Parse(read_str_array[countup_i]); } return return_int_array; }
    static int[,] inta2(int num_array,int in_array){ int[,] int_array2 = new int[num_array,in_array]; for(int i=0;i<num_array;i++){ int[] temp_array = inta(); for(int j=0;j<in_array;j++){ int_array2[i,j] = temp_array[j]; } } return int_array2; }
    static long[] longa(){ string[] read_str_array = ReadLine().Split(' '); long[] return_long_array = new long[read_str_array.Length]; for(long countup_i=0;countup_i<read_str_array.Length;countup_i++){ return_long_array[countup_i] = long.Parse(read_str_array[countup_i]); } return return_long_array; }
    static double[] doublea(){ string[] read_str_array = ReadLine().Split(' '); double[] return_double_array = new double[read_str_array.Length]; for(long countup_i=0;countup_i<read_str_array.Length;countup_i++){ return_double_array[countup_i] = long.Parse(read_str_array[countup_i]); } return return_double_array; }
    // A/B小数点以下切上
    static long divideup(long divided,long divid){ long temp_divide = divided/divid; if(divided % divid > 0){ temp_divide++; } return temp_divide; }
    static long GCD(long a,long b){ if(a < b){ long temp = a; a = b; b = temp; } if(a % b == 0){ return b; } else{ long temp = b; b = a%b; a = temp; return GCD(a,b); } }
    static long LCM(long a,long b){ return a * b / GCD(a,b); }
}
//知見
// (string) hogestr -> (char[]) hoge
    // char hoge = hogestr.ToCharArray();
// (char[]) hoge -> (string) hogestr
    // string hoge = new string(hoge);
// Hashtable ×  Dictionary ○
// Dictionary hoge<string,int>
    // hoge.ContainsKey(string) -> return boolean
    // hoge[string] -> return int
    // hoge[int] -> CE
// Dictionary hoge<int1,int2>
    // hoge<int1,int2>: hoge[int1] -> return int2
    // KeyValuePair<int,int> k <-> k.Key == int1 / k.Value == int2
// SortedDictionary() > SortedList() ???
// キュー　-> 幅優先 ???
// スタック -> 深さ優先 ???
// if (list?.Count > 0) リストが空でもnullでもない