n, m = map(int, input().split())

ans = ["#"]*n

for i in range(m):
    s, c = map(int, input().split())
    if ans[s-1] == "#" or ans[s-1] == c:
        ans[s-1] = c
    else:
        print(-1)
        exit()
if ans[0] == "#":
    ans[0] = 1
elif ans[0] == 0:
    print(-1)
    exit()

print("".join(map(str, ans)).replace("#", "0"))