def solution():
    n, m = map(int, input().split())
    cs = [list(map(int, input().split())) for i in range(m)]
    if m == 0:
        if n > 1:
            print("-1")
        else:
            print("0")
        return
    ans = [-1 for i in range(n)]
    for w in cs:
        s, c = w[0], w[1]
        if (s == 1) and (c == 0) and (n > 1):
            print('-1')
            return
        if ans[s-1] == -1:
            ans[s-1] = c
        elif ans[s-1] != c:
            print('-1')
            return
    ansb = [str(i) if i != -1 else str(0) for i in ans]
    if (ansb[0] == '0') and (len(ansb) > 1):
        ansb[0] = '1'
    anss = ''
    for s in ansb:
        anss = anss + s
    print(int(anss))

solution()
