#include<iostream>
#include<vector>
#include<map>

using namespace std;


int main() {
	int n, m;
	int s, c;

	cin >> n >> m;
	vector<int> checker(n);
	for (int i = 0; i < n; i++) checker[i] = -1;

	for (int i = 0; i < m; i++) {
		cin >> s >> c;
		if (s == 1 && c == 0) {
			cout << "-1" << endl;
			return 0;
		}

		if (checker[s - 1] == -1) {
			checker[s - 1] = c;
		}
		else if (checker[s-1] != c) {
			cout << "-1" << endl;
			return 0;
		}
	}
	int ans = 0;
	for (int i = 0; i < n; i++) {
		if (checker[i] == -1) checker[i] = 0;
		ans += checker[i] * pow(10, n - i - 1);
	}
	cout << ans << endl;
	return 0;
}