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.