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())
a=[-1]*n
v=[0]*n
f=0
for _ in range(m):
	s,c=map(int,input().split())
	if(v[s-1]==0 or a[s-1]==c):
		v[s-1]=1
		a[s-1]=c
	else:
		f=1
s1='a'
if n!=1 and a[0]==-1:
	a[0]=1
for x in a:
	if x==-1:
		x=0
	s1+=str(x)
if f==1 or (n!=1 and s1[1]=='0'):
	print(-1)
else:
	print(s1[1:])
