n,m = map(int,input().split())
x = [tuple(map(int,input().split())) for i in range(m)]
f=True
for i in range(0,1001):
    i = str(i)
    if len(i)==n:
        if all([i[t[0]-1]==str(t[1]) for t in x]):
            print(i)
            f=False
            break
if f:
    print(-1)