# n = int(input())
n, m = map(int,input().split())
# l = [[0 for _ in range(n)] for _ in range(n)]
l = []
f = 0

for i in range(m):
    l.append(list(map(int,input().split())))

# print(l)

for i in range(1000):
    si = str(i)
    if len(si) == n:
        for j in range(m):
            print(si, l)
            if si[l[j][0]-1] == str(l[j][1]):
                print('OK')
                f = 0
            else:
                f = 1
                break
    else:
        continue
    if f == 0:
        print(si)
        exit()

print(-1)