#include <bits/stdc++.h>

using namespace std;

int main()
{
	int N, M;
	cin >> N >> M;

	int s[5], c[5];
	for (int i = 0; i < M; i++) {
		cin >> s[i] >> c[i];
	}

	for (int i = 0; i < M-1; i++) {
		for (int j = i+1; j<M; j++) {
			if ((s[i] == s[j]) && c[i] != c[j] ) {
				cout << "-1" << endl;
				return 0;
			}
			if (s[i] == s[j]) {
				c[i] = 0;
			}
		}
	}

	int res = 0;
	for (int i = 0; i < M; i++) {
		int _keta = 0; 
		if (3 - s[i] == 2) { _keta = 100; }
		if (3 - s[i] == 1) { _keta = 10; }
		if (3 - s[i] == 0) { _keta = 1; }
		res += (c[i] * _keta);
	}

	if (to_string(res).length != N) {
		if (N == 3) {res += 100;}
		if (N == 2) {res += 10;}
	}

	if (res == 0) {
		cout << "-1" << endl;
	} else {
		cout << res << endl;
	}
}
