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 num[5];
int main()
{
	memset(num,-1,sizeof(num));
	int n,m,i,x,y;
	cin>>n>>m;
	for(i=0;i<m;i++)
	{
		cin>>x>>y;
		if(num[x]!=-1&&num[x]!=y||x==1&&!y&&n!=1)
		{
			cout<<-1;
			return 0;
		}
		num[x]=y;
	}
	if(n==1&&num[1]==-1)
	{
		cout<<0;
		return 0;
	}
	if(num[1]==-1)
		cout<<1;
	else
		cout<<num[1];
	for(i=2;i<=n;i++)
		if(num[i]==-1)
			cout<<0;
		else
			cout<<num[i];
	return 0;
}