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

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.

Constraints

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

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

见题面 Input 部分

见题面 Output 部分