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-----
3 3
1 7
3 2
1 7

-----Sample Output-----
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.

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