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 <stdio.h>
int n, m, s, c, e;
int a[10];
int main() {
	scanf("%d%d", &n, &m);
	for (int i = 0; i <= n; i++) {
		a[i] = 10;
	}
	for (int i = 0; i < m; i++) {
		scanf("%d%d", &s, &c);
		if (s == 1 && c == 0 && n != 1)e = 1;
		if (a[s] != 10 && a[s] != c)e = 1;
		a[s] = c;
	}
	if (e)printf("-1\n");
	else {
		for (int i = 1; i <= n; i++) {
			if (a[i] == 10 && !(i == 1 && n != 1))a[i] = 0;
			if (i == 1 && a[i] == 10 && n != 1)a[i] = 1;
			printf("%d", a[i]);
		}
		printf("\n");
	}
}