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<bits/stdc++.h>
using namespace std;
int a[4];
int main()
{
	int n,m;
	cin>>n>>m;
	if(n==1&&m==0)
	{
		cout<<"0\n";
		return 0;
	}int c,d;
	for(int i=1;i<=m;i++)
	{
		
		cin>>c>>d;
		if(a[c]!=0&&a[c]!=d)
		{
			cout<<"-1\n";
			return 0;
			break;
		}
		a[c]=d;
		if(c==1&&d==0&&n!=1)
		{
			cout<<"-1\n";
			return 0;	
			break;
		} 
	}
	if(n==1&&m==1&&c==1&&d==0)
	{
			cout<<"0"<<endl;
			return 0;}
	for(int i=1;i<=n;i++)
	{
		if(a[1]==0)
			a[1]=1;
		cout<<a[i];
	}
	return 0;
}