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