#include<iostream>
using namespace std;
int a[4] = { -1,-1,-1,-1 };
int main() {
	int n, m;

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

	for (int i = 1; i <= n; i++) {
		if (a[i] == -1) {
			a[i] = 0;
		}
	}
	if (a[1] == 0 && n > 1) {
		a[1] = 1;
	}
	for (int i = 1; i <= n; i++) {
		cout << a[i];
	}

}