#include<bits/stdc++.h>
using namespace std;
int main() {
	int n, m;cin >> n >> m;
	vector<int> d(n, -1);
	bool b = true;
	for (int i = 0; i < m; ++i) {
		int s, c;cin >> s >> c;
		if (d[s-1] != -1 && d[s-1] != c) b = false;
		else if (s == 1 && c == 0 && n > 1) b = false;
		else d[s-1] = c;
	}
	if (!b) {
		cout << "-1\n";
		exit(0);
	}
	if (d[0] == -1 && d.size() > 1) d[0] = 1;
	for (int i = 0; i < n; ++i) 
		if (d[i] == -1) d[i] = 0;
	for (int u : d) cout << u;
}