import java.util.Scanner;

class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
	int N =  sc.nextInt();
	int M =  sc.nextInt();
	int[] z = new int[N];

	for (int i = 0; i < M; i++){
        int s = sc.nextInt();
        int c = sc.nextInt();
        if ((z[s-1] != 0 && z[s-1] != c) || (N >= 2 && s == 1 && c == 0)){
            System.out.println(-1);
            return;
        }
        z[s-1] = c;
	}
	if (N >= 2 && z[0] == 0){
        z[0] = 1;
    }
	for (int i = 0; i < z.length; i++){
        System.out.print(z[i]);
    }
  }
}