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;
	string str;
	bool jud;
	bool f;

	cin >> N >> M;
	str="000";

	jud=true; f=true;
	for(int i=0; i<M; i++){
		int s,c;
		cin >> s >> c;
		if(s==1)f=false;
		if(str.at(s-1)!='0' && str.at(s-1)!=c+'0'){ jud=false;}
		str.at(s-1)=c+'0';
	}
	if(N>1 && str.at(0)=='0' && f)str.at(0)='1';
	if(str.at(0)=='0' && N!=1){ jud=false; }



	if(jud){
		for(int i=0; i<N; i++)
			cout << str.at(i);
		cout << endl;
	}
	else {cout << "-1" << endl;}
}