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,s,c,a[5];
	cin>>n>>m;
	for(int i=0;i<=5;i++){
		a[i]=10;
	}
	for(int i=0;i<m;i++){
		cin>>s>>c;
		if(a[s-1]!=c && a[s-1]!=10){
			cout<<"-1"<<endl;
			return(0);
		}
		else{
			a[s-1]=c;
		}
	}
	if(a[0]==0 && n!=1){
		cout<<"-1"<<endl;
		return(0);
	}
	else{
		for(int i=0;i<n;i++){
			if(a[i]!=10)
			cout<<a[i];
			else if(i==0 && n!=1)
				cout<<"1";
			else
				cout<<"0";
		}
	}
	cout<<endl;
  return(0);
}