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;
	cin>>n>>m;
	int t[m],c[m];
	for(int i=0;i<m;i++){
		cin>>t[i]>>c[i];
	}
	int ret=-1;
	for(int i=0;i<1000;i++){
		string s=to_string(i);
		if(s.length()!=n)continue;
		bool val=true;
		for(int j=0;j<m;j++){
			val&=s[t[j]-1]-'0'==c[j];
		}
			if(val){
				ret=i;
				break;
			}
	}
	cout<<ret<<endl;
	return 0;
}