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 main()
{
	int n,m,s,c,a[100];
	cin>>n>>m;
	memset(a,-1,sizeof(a));
	for(int i=1;i<=m;i++)
	{
		cin>>s>>c;
		if(a[s]!=-1&&a[s]!=c)
		{
			cout<<-1<<endl;
			return 0;
		}
		else a[s]=c; 
	}
	if(n>1&&a[1]==0)
	cout<<-1<<endl;
	else if(n==1)
	{
		if(a[1]==-1)
		cout<<0<<endl;
		else
		cout<<a[1]<<endl;
	}
	else
	{
		for(int i=1;i<=n;i++)
		{
		if(i==1&&a[i]==-1)
		cout<<1;
		else if(a[i]==-1)
		cout<<0;
		else
		cout<<a[i];	
		}
	}
	return 0;
}