N, M = map(int, input().split())
cond = [list(map(int, input().split())) for _ in range(M)]
flag = True
ans = [-1]*N

for i in cond:
    digit = i[0]-1
    if digit > N-1:
        flag = False
        break
    elif ans[digit] != -1 and ans[digit] != i[1]:
        flag = False
        break
    elif i == [1, 0]:
        flag = False
        break
    else:
        ans[digit] = i[1]

if flag:
    if ans[0] == -1:
        ans[0] = 1
    
    for i in range(1, N):
        if ans[i] == -1:
            ans[i] = 0
    
    print(''.join(map(str, ans)))
else:
    print(-1)