n, m = map(int, input().split())
a = [-1 for i in range(n)]

for i in range(m):
    s, c = map(int, input().split())
    if a[s - 1] == -1:
        a[s - 1] = c
    elif a[s - 1] == c:
        pass
    else:
        print('-1')
        exit()

if n == 1 and a[0] == 0:
    print('0')
    exit()
if n != 1 and a[0] == 0:
    print('-1')
    exit()

for i in range(n):
    if a[i] == -1:
        a[i] = 0

if a[0] == 0:
    a[0] = 1
ans = ''
for i in range(n):
    ans += str(a[i])
print(ans)