n,m = map(int,input().split())
ans = []

for i in range(m):
    s,c = map(int,input().split())
    li.append([s,c])

for i in range(10**(n-1),10**n):
    buf = str(i)
    flag = True
    for j in range(len(li)):
        if buf[li[j][0]-1] != str(li[j][1]):
            flag = False
    if flag:
        ans.append(buf)
        flag = True

ans.sort()
if ans:
    print(ans[0])
else:
    print(-1)
