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.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		try(Scanner sc = new Scanner(System.in)) {
			
			int n = sc.nextInt();
			int m = sc.nextInt();
			
			Map<Integer, Integer> conditions = new HashMap<>();
			
			boolean ok = true;
			for(int i = 0 ; i < m ; i++ ) {
				int s = sc.nextInt();
				int c = sc.nextInt();
				if ( conditions.containsKey(s)) {
					int v = conditions.get(s);
					
					if ( c != v ) {
						ok = false;
						break;
					}
				}
				else {
					conditions.put(s, c);
				}
			}
			
			if ( ok ) {
				
				if ( n > 1 ) {
					if ( conditions.containsKey(1) && conditions.get(1) == 0 ) {
						System.out.println("-1");
						return;
					}
					else if ( !conditions.containsKey(1) ) {
						conditions.put(1, 1);
					}
				}
				
				StringBuilder sb = new StringBuilder();
				for(int i = 0 ; i < n ; i++ ) {
					int c = conditions.containsKey(i+1) ? conditions.get(i+1) :0;
					sb.append(c);
				}
				System.out.println(sb);

			}
			else {
				System.out.println("-1");
			}
			
		}
	}
}