include <iostream>
#include <vector>
#include <map>
#include <cmath>
int main()
{
	int N, M;
	std::cin >> N >> M;
	std::map<int, int> answer;
	for (int i = 0; i < N+1; i++)
	{
		answer[i] = -1;
	}
	for (int i = 0; i < M; i++)
	{
		int index, value = 0;
		std::cin >> index >> value;
		if (answer.find(index) != answer.end() && answer[index] != -1 && answer[index] != value)
		{
			std::cout << -1;
			return 0;
		}
		answer[index] = value;
	}
	if (answer[1] == 0 || answer[1] == -1)
	{
		std::cout << -1;
		return 0;
	} else if(answer[1] == -1)
	{
		answer[1] = 1;
	}
	int sum = 0;
	for (int i = 1; i < N + 1; i++)
	{
		if (answer[i] != -1)
			sum += answer[i] * std::pow(10, N - i);
	}
	std::cout << sum;
	return 0;
}