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,a[5]={0,-1,-1,-1},l,r;
	cin>>n>>m;
	int ok=1;
	for(int i=0;i<m;i++){
		cin>>l>>r;
		if(a[l]!=-1&&a[l]!=r) ok=0;
		else a[l]=r;
	}
	if(a[1]==0&&n!=1)ok=0;
	if(ok){
		if(a[1]==-1&&n==1) a[1]=0;
		else if(a[1]==-1) a[1]=1;
		for(int i=1;i<=n;i++){
			if(a[i]==-1) a[i]=0;
			cout<<a[i];
		}
	}
	else cout<<-1;
	cout<<endl;
	return 0;
}