n,m = list(map(int,input().split()))
ans = [-1]*n
if m == 0:
    print(0)
else:
    for i in range(m):
        s,c = list(map(int,input().split()))
        if ans[s-1] != -1 and ans[s-1] != c:
            ans = -1
            break
        ans[s-1] = c
        if s == 1 and n != 1 and c == 0:
            ans = -1
            break        
    if ans != -1:
        for i in range(n):
            if ans[i] == -1:
                ans[i] = '0'
            else:
                ans[i] = str(ans[i])
        print(''.join(ans))
    else:
        print(ans)