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 nummax =1;
        for(int i=0;i<num[0];i++){
            nummax*=10;
        }
        int nummin =nummax/10;
        if(nummin == 1){
            nummin = 0;
        }
        int[,] jd = inta2(num[1],2);
        /*
        for(int i=0;i<num[1];i++){
            WriteLine(jd[i,1]);
        }
        */
        int ans = -2;
        for(int i=0;i<num[1]-1;i++){
            for(int j=i+1;j<num[1];j++){
                if(jd[i,0] == jd[j,0]){
                    if(jd[i,1] != jd[j,1]){
                        ans = -1;
                    }
                }
            }
        }
        if(ans == -1){
            WriteLine(ans);
        }else{
            ans = -1;
            //nummin = 700;
            //nummax = 705;
            for(int i=nummin;i<nummax;i++){
                int count = 0;
                //WriteLine(i);
                for(int j=0;j<num[1];j++){
                    if(jd[j,0] == 1){
                        int check = i/nummin;
                        if(jd[j,1] == check){
                            //WriteLine(111);
                            count++;
                        }
                    }else if(jd[j,0] == 2){
                        int check = (i%100)/10;
                        if(jd[j,1] == check){
                           // WriteLine(222);
                            count++;
                        }
                    }else if(jd[j,0] == 3){
                        int check = i%10;
                        //WriteLine(jd[j,1]);
                        //WriteLine(check);
                        if(jd[j,1] == check){
                            //WriteLine(333);
                            count++;
                        }
                    }
                }
                //WriteLine(count);
                if(count == num[1]){
                    ans = i;
                    break;
                }
            }
            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
