#!/usr/bin/env python

def func():
    n,m = [int(i) for i in input().split(" ")]
    pibot = 10**(m-1)
    dic = {}

    for i in range(m):
        tmp = [int(i) for i in input().split(" ")]

        if tmp[0] not in dic.keys():
            dic[tmp[0]] = tmp[1]
        else:
            if dic[tmp[0]] != tmp[1]:
                print("-1")
                return

    a = [0] * m
    for key in dic.keys():
        print(key)
        a[key-1] = dic[key]

    tmp_s = ""
    for i in a:
        tmp_s += str(i)

    if int(tmp_s) < pibot:
        print("-1")
        return
    else:
        print(tmp_s)

    print("")

if __name__ == "__main__":
    func()