n, m = map(int, input().split())
ans = [-1 for i in range(n)]
for i in range(m):
    s, c = map(int, input().split())
    if s == 1 and c == 0:
        print(-1)
        exit()
    if ans[s-1] != -1 and ans[s-1] != c:
        print(-1)
        exit()
    ans[s-1] = c

for i in range(n):
    if ans[0] == -1:
        ans[0] = 1
    elif ans[i] == -1:
        ans[i] = 0

print(int("".join(map(str, ans))))