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;
	bool check = true;
	
	int s,c, a[5] = {0, -1, -1, -1};
	for (int i = 0; i < m; i++) {
		cin >> s >> c;
		if (a[s] != -1 && a[s] != c) check = false;
	    else a[s] = c;
	}   
	if (a[1] == 0 && n != 1) check = false;
	if (check) {
		if (a[1] == -1 && n == 1) a[1] = 0;
		else if (a[1] == -1) a[1] = 1;
		for (int i = 1; i <= n; i++) {
			if (a[i] == -1) a[i] = 0;
			cout << a[i];
		} 
	} else cout << -1;
	
	return 0;
}