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>
#include<iostream>
using namespace std;
const int MAX=1e9+7;
const int mod=1e9+7;
int a[5],s,c,flag=0;

int main()
{
	ios::sync_with_stdio(0);cin.tie(0); 
	memset(a,-1,sizeof(a));
	int n,m;
	cin>>n>>m;	
	for(int i=0;i<m;i++)
	{
		cin>>s>>c;
		if(a[s-1]==-1)
		{
			a[s-1]=c;
		}
		else if(a[s-1]!=c)
		{
			flag=1;
		}	
	}
	if(flag||a[0]==0&&n!=1)
	cout<<-1;
	else{
		
		for(int i=0;i<n;i++)
		{
			if(i==0&&a[i]==-1&&n!=1)cout<<1;
			else if(a[i]==-1)cout<<0;
			else cout<<a[i];	
		}
	}
}

