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<iostream>
#include<algorithm>
#include<string>
using namespace std;
int main(){
	int N,M,a[3]={-1,-1,-1},n=0,s,c;
	cin>>N>>M;
	for(int i=0;i<M;i++){
		cin>>s>>c;s--;
		if(a[s]==-1)a[s]=c;
		else if(a[s]!=c){cout<<-1;return 0;}
	}
	for(int i=0;i<N;i++){
		if(a[i]==-1){
			if(i!=0 || (i==0&&N==1))a[i]=0;
			else a[i]=1;
		}
	}
	for(int i=0;i<N;i++){
		n*=10;
		n+=a[i];
	}
	if(N>1&&a[0]==0)cout<<-1;
	else cout<<n;
	return 0;
}