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<iostream>
#include<cstdio>
#include<string.h>
using namespace std;
char s[10];
int a[10];
int n,m,x,c;
int main()
{
	cin>>n>>m;
	bool flag=1;
	memset(a,-1,sizeof(a));
	for(int i=1;i<=m;i++)
	{
		scanf("%d%d",&x,&c);
		if(a[x]!=-1&&a[x]!=c)
			flag=0;
		a[x]=c;
	}
	if(n!=1&&a[1]==0)
		flag=0;
	if(!flag)
	{
		cout<<-1;
	}
	else
	{
		if(n==1)
		{
			cout<<max(0,a[1]);
		 } 
		 else
		 {
			for(int i=1;i<=n;i++)
			{
				if(i==1)
					cout<<max(1,a[i]);
				else
					cout<<max(0,a[i]);
			}
		}
	}
	return 0;
} 