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.Arrays;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Main mainObj = new Main();
		mainObj.solve();
	}
	
	public void solve() {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt();
		
		int[] ansArr = new int[n];
		Arrays.fill(ansArr, -1);
		
		int m = sc.nextInt();
		for(int i = 0 ; i < m; i++) {
			int s = sc.nextInt();
			int c = sc.nextInt();
			
			if(ansArr.length > 1 && s == 1 && c == 0) {
				System.out.println(-1);
				sc.close();
				return;
			}
			if(ansArr[s-1] >= 0 && ansArr[s-1] != c) {
				System.out.println(-1);
				sc.close();
				return;
			}
			ansArr[s-1] = c;
		}
		
		for(int i = 0; i < n ; i++) {
			if(ansArr[i] < 0) {
				if(i == 0 && ansArr.length > 1) {
					System.out.print(1);
				}else {
					System.out.print(0);
				}
			}else {
				System.out.print(ansArr[i]);
			}
		}
		
		System.out.print("\n");
		
		sc.close();
	}
}
