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 ans[s-1] == -1:
        ans[s-1] = c
    else:
        if ans[s-1] == c:
            pass
        else:
            ans = -1

if type(ans) != list:
    print(ans)
else:
    if n > 1 and ans[0] == 0:
        ans = -1
        print(ans)
    else:
        for i in range(n):
            if ans[i] == -1:
                if i == 0:
                    ans[i] = 1
                else:
                    ans[i] = 0
        print(''.join(map(str, ans)))