N, M = list(map(int, input().split()))
result = ["x"] * N
no_break_check = 1
for i in range(M):
    s, c = list(input().split())
    s = int(s)
    if result[s-1] == "x":
        result[s-1] = c
    elif result[s-1] != c:
        print("-1")
        no_break_check = 0
        break
if no_break_check:
    for i, chr in enumerate(result):
        if result[i] == "x":
            if i == "0":
                result[i] = "1"
            else:
                result[i] = "0"
    if result[0] == "0":
        print("-1")
    else:
        print(int("".join(result)))