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();
        int[] num = new int[n];
        int flag = 0;
        for (int i = 0; i < m; i++) {
            int s = sc.nextInt();
            int c = sc.nextInt();
            if(s == 1 && c ==0 && n != 1 || num[s - 1] != 0 && num[s - 1] != c){
                flag = 1;
            }else{
                num[s - 1] = c;
            }
        }
        if(flag == 1){
            System.out.println("-1");
        }else{
            if(num[0] == 0 && n != 1){
                num[0] = 1;
            }
            for (int i = 0; i < n; i++) {
                System.out.print(num[i]);
            }
        }
    }
}