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.*;
    public class Main {
     
    	public static void main(String[] args) {
    		Scanner scan = new Scanner(System.in);
    		int n=Integer.parseInt(scan.next());
    		int m=Integer.parseInt(scan.next());
    		
    		int[] memo =new int[n];
    		Arrays.fill(memo, -1);
    		boolean ans =true;
    		int s,c;
    		for (int i=0;i<m;++i) {
    			s=Integer.parseInt(scan.next());
    			c=Integer.parseInt(scan.next());
    			
    			if (s==1 && c==0 && n!=1) {
    				ans=false;
    				break;
    			}else {
    				if (memo[s-1]==-1 || memo[s-1]==c) {
    					memo[s-1]=c;
    				}else {
    					ans=false;
    					break;
    				}
    				
    			}
    			
    		}
    		if (ans) {
    			if(memo[0]==-1&&n!=1) {
    				memo[0]=1;
    			}
    			for (int i:memo) {
    				if (i!=-1) {
    					System.out.print(i);
    				}else {
    					System.out.print(0);
    				}
    			}
    		}else {
    			System.out.print(-1);
    		}
    		
    		
    }	
    }
// end 