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;
import java.util.List;
import java.util.ArrayList;
 
public class Main {
  
  static int N,M;
  
  static List<Integer> s = new ArrayList<>();
  static List<Integer> c = new ArrayList<>();
  
 public static void main(String[] args){
   Scanner scanner = new Scanner(System.in);
   N = scanner.nextInt();
   M = scanner.nextInt();
   for(int i = 0;i < M;i++){
     s.add(scanner.nextInt());
     c.add(scanner.nextInt());
   }
   System.out.println(solve());
 }
  
  public static String solve(){
    for(int i = 0;i < 1000;i++){
      String str = String.valueOf(i);
      if(ok(str))return str;
    }
    return "-1";
  }
  
  public static boolean ok(String str){
    if(str.length() != N) return false;
    for(int i = 0;i < M;i++){
      if(str.charAt(s.get(i) - 1) != (char)((int)c.get(i) + '0')) return false;
    }
    return true;
  }
}