n,m=map(int,input().split())
sc = [tuple(map(int,input().split())) for _ in range(m)]

for i in range(10**n):
    if len(str(i))!=n:
        continue
    for j in range(m):
        if all([str(i)[s-1] == str(c) for s,c in sc]):
            print(i)
            exit()
print(-1)
