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;
 
signed main () {
	int n, m;
	cin >> n >> m;
	vector < int > a(n, -1);
	bool shit = 0;
	for (int i = 0; i < m; ++i) {
		int s, x;
		cin >> s >> x;
		--s;
		if (a[s] != -1 && a[s] != x) 
			shit = 1;
		else
			a[s] = x;
	}
	if (a[0] == 0 && n != 1)
		shit = 1;
	if (shit)
		cout << "-1\n";
	else {
		for (int i = 0; i < n; ++i) {
			if (a[i] == -1) {
				if (i || n == 1)
					cout << '0';
				else
					cout << '1';
			}
			else 
				cout << a[i];
		}
		cout << '\n';
	}
}
