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 n, m;
int a[23];
bool b[23];
bool fl = 1;

int main() {
	cin >> n >> m;
	while(m--) {
		int x, y;
		cin >> x >> y;
		if(a[x] != 0 && a[x] != y) {
			fl = 0;
			break;
		}
		a[x] = y;
		b[x] = 1;
	}
	if(!fl) {
		cout << "-1";
		return 0;
	}
	if(n != 1 && !a[1]) {
		if(b[1]) {
			cout << "-1";
			return 0;
		}
		else a[1] = 1;
	}
	for(int i = 1; i <= n; ++i)
		cout << a[i];
	return 0;
}