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 <vector>

using namespace std;

int main(){
	int n,m;
	cin >> n >> m;
	bool res = true;
	vector<int> tmp(n,11);
	for(int i=0;i<m;++i){
		int a,b;
		cin >> a >> b;
		if(n > 1 && a == 1 && b == 0){
			res = false;
		}else if(tmp[a-1] == 11){
			tmp[a-1] = b;
		}else if(tmp[a-1] != b){
			res = false;
		}
	}
	if(res){
		for(int i=0;i<n;++i){
			if(tmp[i]==11){
				if(i==0 && n != 1)cout << 1;
				else cout << 0;
			}
			else cout << tmp[i];
		}
	}else{
		cout << -1;
	}
	cout << endl;
}