#! env/bin/local python3
# -*- coding: utf-8 -*-

n, m = map(int, input().split())
conditions = []
while True:
    try:
        conditions.append(list(map(int, input().split())))
    except EOFError:
        break


for i in range(10**(n-1), 10**n):
    flag = True
    for c in conditions:
        if str(i)[c[0]-1] != str(c[1]):
            flag = False

    if flag:
        print(i)
        break
else:
    print(-1)




