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>
using namespace std;
int main()
{
	int a[4]={0};
	int n,m;
	cin>>n>>m;
	int vis[4]={0};
	for(int i=1;i<=m;++i)
	{
		int l,r;
		cin>>l>>r;
		if(vis[l]&&a[l]!=r){cout<<-1;return 0;}
		else {a[l]=r;vis[l]=1;}
	}
	if(n>1&&vis[1]&&a[1]==0){cout<<-1;return 0;}
	if(n==1&&a[1]==0){cout<<0;return 0;}
	if(n>1&&a[1]==0)a[1]=1;
	for(int i=1;i<=n;++i)cout<<a[i];
}