/*input
1 1
1 0
*/
#include <bits/stdc++.h>
using namespace std;
#define MAX 5

int a[MAX] = {}, vis[MAX] = {};
int n, m;

int main() {
	cin >> n >> m;
	for (int i = 1; i <= m; i++) {
		int p, x; cin >> p >> x;

		if (vis[p] && a[p] != x) {
			cout << -1 << '\n';
			return 0;
		}
		if (p == 1 && x == 0 && n != 1) {
			cout << -1 << '\n';
			return 0;
		}

		vis[p] = 1;
		a[p] = x;
	}
	if (!vis[1] && n != 1) a[1] = 1;

	for (int i = 1; i <= n; i++) cout << a[i];
	cout << '\n';
	return 0;
}