n, m = map(int, input().split())
ans = [-1 for _ in range(n)]
end_flag = False
for _ in range(m):
    s, c = map(int, input().split())
    if ans[s-1] == -1:
        ans[s-1] = c
    elif ans[s-1] == c:
        continue
    else:
        end_flag = True
        break
# print(ans)
if ans[0] == 0:
    end_flag = True
if ans[0] == -1:
    ans[0] = 1

for i in range(1, n):
    if ans[i] == -1:
        ans[i] = 0
# print(ans)
if end_flag:
    print(-1)
else:
    ss = ''
    for i in ans:
        ss = ss + str(i)
    print(ss)
