import java.util.Arrays;
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];
		Arrays.fill(num, -1);
		boolean ableFlg = true;

		if (N == 1 && M == 0) {
			System.out.print(0);
		}else if(N == 1 && M == 1){
			int insert = sc.nextInt();
			int number = sc.nextInt();
			System.out.println(number);
		}else {
			for (int i = 0; i < M; i++) {
				int insert = sc.nextInt();
				int number = sc.nextInt();

				if (insert == 1 && number == 0) {
					ableFlg = false;
					break;
				}

				if (num[insert - 1] != -1 && num[insert - 1] != number) {
					ableFlg = false;
					break;
				}

				num[insert - 1] = number;

			}

			if (ableFlg) {
				for (int i = 0; i < N; i++) {
					if (num[0] == -1) {
						num[0] = 1;
					}

					if (num[i] == -1) {
						System.out.print(0);
					}else {
						System.out.print(num[i]);
					}
				}
			}else {
				System.out.println(-1);
			}
		}
	}
}