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;
	int s[15],c[15],a[4]={0},b[4]={0},p[4]={0};
	cin>>n>>m;
	int f1=0;
	for(int i=0;i<m;i++){
		cin>>s[i]>>c[i];
		if((b[s[i]]!=c[i]&&p[s[i]])||(s[i]==1&&c[i]==0&&n>1)){
			f1=1;
		}
		a[s[i]]=c[i];
		b[s[i]]=c[i];
		p[s[i]]=1;
	}
	int f2=1;
	if(f1){
		cout<<-1;
	}
	else{
		if(a[1]==0&&n>1)a[1]=1;
		for(int i=1;i<=n;i++)cout<<a[i];
	}
	return 0;
}