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
n,m= map(int,input().split(' '))
arr=[0 for i in range(n)]

im= False
for i in range(m):
	x,y= map(int,input().split(' '))
	if x==1 and y==0 and n>1:
		im=True
	if arr[x-1]!=0 and arr[x-1]!=y:
		im=True
	arr[x-1]=y
if arr[0]==0 and n>1:
	arr[0]=1
if im:
	print(-1)
else:
	print(''.join(str(i) for i in arr))