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>
using namespace std;
int main(){
	int n,m;
	cin>>n>>m;
	string s="";
	for(int i=0;i<n;++i)
		s+='0';
	bool c[n];
	for(int i=0;i<n;++i)
		c[i]=false;
	bool flag=true;
	for(int i=0;i<m;++i){
		int a;
		char cc;
		cin>>a>>cc;
		if(a==1&&cc=='0')
			flag=false;
		if(c[a-1]!=false&&s[a-1]!=cc){
			cout<<-1;
			return 0;
		}
		c[a-1]=true;
		s[a-1]=cc;
	}
	if(s.size()>1&&s[0]=='0'){
		if(flag)
			s[0]='1';
		else{
			cout<<-1;
			return 0;
		}
	}
	cout<<s<<endl;
	return 0;
}