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 main()
{
	int N, M, s[6], c[6];
	scanf ("%d %d", &N, &M);
	for (int i = 0; i < M; i++) scanf ("%d %d", &s[i], &c[i]);

	int p = 1;
	for (int i = 1; i < N; i++) p *= 10;
	for (int d = p - (N == 1); d < p * 10; d++){
		char S[10];
		sprintf(S, "%d", d);
		int g = 0;
		for (int k = 0; k < M; k++){
			if (S[s[k] - 1] == c[k] + '0') g++;
		}
		if (g == M){
			puts(S);
			return 0;
		}
	}
	puts("-1");
	return 0;
}
