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Contest: Task: Related: TaskB TaskD

Score : $300$ points

Problem Statement

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 $c_i$. $\left(i = 1, 2, \cdots, M\right)$

Constraints

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

Input

Input is given from Standard Input in the following format:

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

Output

Print the answer.

Sample Input 1

Sample Output 1

$702$ 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.

Sample Input 2

3 2
2 1
2 3

Sample Output 2

-1

Sample Input 3

3 1
1 0

Sample Output 3

-1