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
#include<stdio.h>
int main()
{
	int n,m,x,y;
	int a[5]={0},b[5]={0};
	scanf("%d%d",&n,&m);
	int flag=1;
	while(m--)
	{
		scanf("%d%d",&x,&y);
		if(b[x]==0||a[x]==y) {a[x]=y;b[x]=1;}
		else flag=0;
	}

	if(flag){
		if(n==1)	printf("%d\n",a[1]);
		else{
			if(a[1]==0&&b[1]==0)	a[1]=1;
			if(a[1]==0&&b[1]==1)
			{
				printf("-1\n");
				return 0;
			}
			for(int i=1;i<=n;i++)
			printf("%d",a[i]);
			printf("\n");
			}
		}
	else printf("-1\n");
	
	return 0;
 } 