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 n,m;
int a[10];
int main(){
	cin>>n>>m;
	memset(a,-1,sizeof a);
	int f=1;
	while(m--){
		int pos,c;
		cin>>pos>>c;
		if(a[pos]!=-1&&c!=a[pos]){
			f=0;
			break;
		}
		else a[pos]=c;
	}
	if(n==1){
		if(a[1]==-1)a[1]=0;
	}
	else{
		if(a[1]==0){
			f=0;
		}
		if(a[1]==-1)a[1]=1;
		for(int i=2;i<=n;i++){
			if(a[i]==-1)a[i]=0;
		}
	}
	if(!f)cout<<"-1"<<endl;
	else{
		for(int i=1;i<=n;i++)cout<<a[i];
		cout<<endl;
	}
	return 0;
} 