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<cstring>
using namespace std;
int main()
{
	int n,m,s,c;
	cin>>n>>m;
	int a[5],b[5],flag=0;
	memset(a,0,sizeof(a));
	memset(b,0,sizeof(b));
	for(int i=0;i<m;i++)
	{
		cin>>s>>c;
		s--;
		if(!b[s])
		{
			a[s]=c;
			b[s]=1;
		}
		else
		{
			if(a[s]!=c)
			  flag=1;
		}
	}
	if(!b[0]&&n>1)
	  a[0]=1;
	if(a[0]==0&&n>1)
	  flag=1;
	if(flag==1)
	{
		cout<<-1<<endl;
		return 0;
	}
	for(int i=0;i<n;i++)
	  cout<<a[i];
	cout<<endl;
	return 0;
}
