#include <bits/stdc++.h>
using namespace std;
 
signed main () {
	int n, m;
	cin >> n >> m;
	vector < int > a(n, -1);
	bool shit = 0;
	for (int i = 0; i < m; ++i) {
		int s, x;
		cin >> s >> x;
		--s;
		if (a[s] != -1 && a[s] != x) 
			shit = 1;
		else
			a[s] = x;
	}
	if (a[0] == 0 && n != 1)
		shit = 1;
	if (shit)
		cout << "-1\n";
	else {
		for (int i = 0; i < n; ++i) {
			if (a[i] == -1) {
				if (i || n == 1)
					cout << '0';
				else
					cout << '1';
			}
			else 
				cout << a[i];
		}
		cout << '\n';
	}
}
