Guess The Number

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.

Examples

Input

3 3 1 7 3 2 1 7

Output

702

Input

3 2 2 1 2 3

Output

-1

Input

3 1 1 0

Output

-1

inputFormat

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

outputFormat

Output

Print the answer.

Examples

Input

3 3 1 7 3 2 1 7

Output

702

Input

3 2 2 1 2 3

Output

-1

Input

3 1 1 0

Output

-1

样例

3 1
1 0

-1