If there is an integer not less than $0$ satisfying the following conditions, print the smallest such integer; otherwise, print -1.

• The integer has exactly $N$ digits in base ten. (We assume $0$ to be a $1$-digit integer. For other integers, leading zeros are not allowed.)
• The $s_i$-th digit from the left is $c_i$. $\left(i = 1, 2, \cdots, M\right)$

Input is given from Standard Input in the following format:

```
$N$ $M$
$s_1$ $c_1$
$\vdots$
$s_M$ $c_M$
```

Print the answer.

-   All values in input are integers.
-   $1 \leq N \leq 3$
-   $0 \leq M \leq 5$
-   $1 \leq s_i \leq N$
-   $0 \leq c_i \leq 9$

702

$702$ satisfies the conditions - its $1$-st and $3$-rd digits are 7 and 2, respectively - while no non-negative integer less than $702$ satisfies them.