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

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] ary = new int[n];
		for(int i = 0; i < n; i++){
			ary[i] = -1;
		}
		int m = sc.nextInt();
		boolean isPossible = true;
		for(int i = 0; i < m; i++){
			int s = sc.nextInt();
			int c = sc.nextInt();
			if(ary[s - 1] != c && ary[s - 1] != -1){
				isPossible = false;
			}else{
				ary[s - 1] = c;
			}
		}
		if(n > 1 && ary[0] == 0){
			isPossible = false;
		}
		if(ary[0] == -1){
			if(n == 1){
				ary[0] = 0;
			}else{
				ary[0] = 1;
			}
		}
		for(int i = 1; i < n; i++){
			if(ary[i] == -1){
				ary[i] = 0;
			}
		}
		String ans = "";
		for(int i = 0; i < n; i++){
			ans += ary[i];
		}
		System.out.println(isPossible ? ans : "-1");
	}
}
