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.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {

	static int[] S ;
	public static void main(String[] args) throws Exception {
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		String W = in.readLine();
		String[] Ws = W.split(" ");
		int N = Integer.parseInt(Ws[0]);
		int M = Integer.parseInt(Ws[1]);

		String[] S = new String[(int)Math.pow(10, N)];
		for(int i=0;i<S.length;i++){
			S[i] = String.valueOf(i);
		}

		String[][] Q = new String[M][];
		for(int i=0;i<M;i++){
			W = in.readLine();
			Q[i] = W.split(" ");
		}

		int i = (int)Math.pow(10, N-1);
		int end = i*10;
		if(i==1){
			i=0;
		}
		for(;i<end;i++){
			boolean flg = true;
			for(int k = 0;k<Q.length;k++){
				if(S[i].charAt(Integer.parseInt(Q[k][0])-1) != Q[k][1].charAt(0)){
					flg= false;
					break;
				}
			}
			if(flg){
				break;
			}
		}
		if(i==end){
			System.out.println(-1);
		}else{
			System.out.println(S[i]);
		}
	}


}
