import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int m = scan.nextInt();
        int[] s = new int[m];
        int[] c = new int[m];

        for(int i = 0; i < m; i++) {
        	s[i] = scan.nextInt();
        	c[i] = scan.nextInt();

        	if(n != 1) {
        		if(s[i] == 1 && c[i] == 0) {
        			System.out.println(-1);
        			return;
        		}
        	}
        }


        if(n == 3) {

        	for(int i = 1; i < 9; i++) {
        		for(int j = 0; j < 9; j++) {
        			for(int k = 0; k < 9; k++) {
        				int[] temp = {i, j, k};
        				int ans = i * 100 + j * 10 + k;
        				boolean f = true;
        				for(int l = 0; l < m; l++) {
        					if(temp[s[l] - 1] != c[l]) {
        						f = false;
        						break;
        					}
        				}
        				if(f) {
        					System.out.println(ans);
        					return;
        				}
        			}
        		}
        	}
        }
        if(n == 2) {
        		for(int j = 1; j < 9; j++) {
        			for(int k = 0; k < 9; k++) {
        				int[] temp = {j, k};
        				int ans = j * 10 + k;
        				boolean f = true;
        				for(int l = 0; l < m; l++) {
        					if(temp[s[l] - 1] != c[l]) {
        						f = false;
        						break;
        					}
        				}
        				if(f) {
        					System.out.println(ans);
        					return;
        				}
        			}
        		}
        }
        if(n == 1) {
    			for(int k = 0; k < 9; k++) {
    				int[] temp = {k};
    				int ans = k;
    				boolean f = true;
    				for(int l = 0; l < m; l++) {
    					if(temp[s[l] - 1] != c[l]) {
    						f = false;
    						break;
    					}
    				}
    				if(f) {
    					System.out.println(ans);
    					return;
    				}
    			}
        }
        System.out.println(-1);
    }
}