nm = input()
n, m = nm.split(' ')

data = []
for i in range(int(m)):
    tmp = input()
    n1, n2 = tmp.split(' ')
    data.append([int(n1), int(n2)])

ans = {}

try:
    for target in data:
        if target[0] > int(n):
            exit(1)
        if target[0] not in ans.keys():
            ans[target[0]] = target[1]
        elif ans[target[0]] is not target[1]:
            exit(1)

    if ans[1] is 0:
        exit(1)

    keys = ans.keys()

    res = 0
    for key in keys:
        tmp = 10 ** (int(n) - int(key))
        a = tmp *  int(ans[key])
        res += a

    print(res)
except:
    print(-1)
