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 m,n;
	cin>>m>>n;
	int a[m+1];
	int f=0;
	for(int i=1;i<=m;i++)
	{
		a[i]=-1;
	}
	for(int i=1;i<=n;i++)
	{
		int x,y;
		cin>>x>>y;
		if(a[x]==-1 || a[x]==y)
		a[x]=y;
		else
		f=1;
	}
	if(a[1]==0)
	f=1;
	if(m==1 && a[1]==-1)
	a[1]=0;
	else if(a[1]==-1)
	a[1]=1;
	
	if(m==1 && a[1]==0)
	f=0;
	if(f==1)
	{
		cout<<"-1";
		return 0;
	}
	for(int i=1;i<=m;i++)
	{
		if(a[i]==-1)
		a[i]=0;
		cout<<a[i];
	}
	return 0;
 } 