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 ans[10];
int n,m;
int main(){
	cin>>n>>m;	
	for(int i=1;i<=m;i++){
		int s,c;
		cin>>s>>c;
		if(s==1&&c==0&&n>1){ cout<<-1;return 0;}
		else if(ans[s-1]==0|| ans[s-1]==c) ans[s-1]=c;
		else { cout<<-1;return 0;}
	}
	if(n==1) cout<<ans[0];
	else 
	{
		if(ans[0])cout<<ans[0];
		else cout<<1;
		for(int i=1;i<n;i++) cout<<ans[i];
	}
}