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

3 3
1 7
3 2
1 7

Sample Output 1

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.

Sample Input 2

3 2
2 1
2 3

Sample Output 2

-1

Sample Input 3

3 1
1 0

Sample Output 3

-1