
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int m = scanner.nextInt();
        Integer[] digits = new Integer[n];
        for (int i = 0; i < m; i++) {
            int s = scanner.nextInt()-1;
            int c = scanner.nextInt();
            if(digits[s]==null){
                digits[s]=c;
            }else{
                if(digits[s]!=c){
                    System.out.println(-1);
                    return;
                }
            }
        }
        if(digits[0]==0 && n!=1){
            System.out.println(-1);
            return;
        }else if(digits[0]==null){
            digits[0] = n==1? 0 : 1;
        }
        for (int i = 1; i < n; i++) {
            if(digits[i]==null){
                digits[i]=0;
            }
        }
        int res = digits[0];
        for (int i = 1; i < n; i++) {
            res = res*10+digits[i];
        }
        System.out.println(res);

    }
}
