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<algorithm>
 using namespace std;
 int a[4];
 int main()
 {
 	int n,m,x,y,flag=0;
 	cin>>n>>m;
	a[1]=a[2]=a[3]=-1;
	for(int i=1;i<=m;i++){
		cin>>x>>y;
		if(a[x]!=-1&&a[x]!=y){
			flag=1;
			break;
		} 
		a[x]=y;
	}
	if(flag==1){
		cout<<-1<<endl;
		return 0;
	}
	if(a[1]==0&&n!=1){
		cout<<-1<<endl;
		return 0;
	}
	if(n==1&&a[1]==-1){
		cout<<0<<endl;
		return 0;
	}
	for(int i=1;i<=n;i++){
		if(a[i]==-1&&i==1){
			cout<<"1";
			continue;
		} 
		if(a[i]==-1) cout<<"0";
		else cout<<a[i];
	}
 }