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 a[10];
bool flag[3][3],check=true;
int main(){
	int n,m;
	cin>>n>>m;
	int c,b;
	for(int i=1;i<=m;i++){
		cin>>c>>b;
		if(a[c]>0&&a[c]!=b) check=false;
		else{
			a[c]=b;
		}
		if(c==1&&b==0&&n>1) check=false;
	}
	if(a[1]==0&&n>1) a[1]=1;
	
	if(!check) cout<<-1;
	else{
		for(int i=1;i<=n;i++) cout<<a[i];
	}
}