#include <bits/stdc++.h>

using namespace std;

int main() {
	int n, m;
	scanf("%d %d", &n, &m);
	vector<int> p{1};
	while(p.size() < n) p.insert(p.begin(), p[0] * 10);

	map<int, int> s;
	int ans = 0;
	while(m--) {
		int a, b;
		scanf("%d %d", &a, &b);
		if(s.count(a)) {
			if(s[a] != b) return printf("-1\n"), 0;
		}
		else {
			s[a] = b;
			ans += b * p[a - 1];
			if(a == 1 and b == 0 and n > 1) return printf("-1\n"), 0;
		}
	}
	if(n > 1 and !s.count(1)) {
		ans += p[0];
	}
	printf("%d\n", ans);
}
