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

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