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 M = sc.nextInt();
    
    if(M==0 && N==1){
   		System.out.println(0);
        return;
    }
    
    
    int[] s = new int[M];
    int[] c = new int[M];
    
    for(int i=0;i<M;i++){
      s[i] = sc.nextInt();
      c[i] = sc.nextInt();
      
      if(N!=1 && s[i] ==1 && c[i] == 0){
   		System.out.println("-1");
        return;      
      }
    }
    
    int[] a = new int[N];
    for(int i=0;i<N;i++){
      a[i] = -1;
    }
    
    for(int k=0;k<M;k++){   
      if(a[s[k]-1] == -1){
        a[s[k]-1] = c[k];
      }
      else if(a[s[k]-1] != c[k]){
        System.out.println("-1");
        return;        
      }

    }
     if(N==1 && a[0]==0){
   		System.out.println(0);
        return;     
     }
     if(a[0]== 0){
   		System.out.println("-1");
        return;
      }
      
      int ans = 0;
    if(a[0] == -1)
      ans += Math.pow(10,N-1);
      for(int j=0;j<N;j++){
        if(a[j] != -1)
      		ans += a[j] * Math.pow(10,N-j-1);
      }
      
      System.out.println(ans);
      return;
  }
}
