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 sc = new Scanner(System.in);
        int N = sc.nextInt();
        int M = sc.nextInt();
        StringBuilder sb = new StringBuilder();
        sb.append('1');
        for (int i=0;i<N-1;i++) {
            sb.append('0');
        }
        boolean[] flag = new boolean[N];
        char[] ans = sb.toString().toCharArray();
        if (N==1 && M==0) {
            System.out.println(0);
            return;
        }
        for (int i=0;i<M;i++) {
            int s = sc.nextInt()-1;
            int c = sc.nextInt();
            if (s==0 && c==0 && N!=1) {
                System.out.println(-1);
                return;
            }
            if (flag[s] && ans[s]!=(char)(c+48)) {
                System.out.println(-1);
                return;
            }
            ans[s] = (char)(c+48);
            flag[s] = true;
        }
        for (int i=0;i<N;i++) {
            System.out.print(ans[i]);
            if (i==N-1) System.out.println("");
        }
    }
}