#include <bits/stdc++.h>
using namespace std;

int main() {
	int n, m;
	cin >> n >> m;
	bool check = true;
	
	int s,c, a[5] = {0, -1, -1, -1};
	for (int i = 0; i < m; i++) {
		cin >> s >> c;
		if (a[s] != -1 && a[s] != c) check = false;
	    else a[s] = c;
	}   
	if (a[1] == 0 && n != 1) check = false;
	if (check) {
		if (a[1] == -1 && n == 1) a[1] = 0;
		else if (a[1] == -1) a[1] = 1;
		for (int i = 1; i <= n; i++) {
			if (a[i] == -1) a[i] = 0;
			cout << a[i];
		} 
	} else cout << -1;
	
	return 0;
}