#include <bits/stdc++.h>
using namespace std;

int main() {
	int n,m;
	cin >> n >> m;
	vector<char> k(n,' ');
	for(int i = 0;i < m;i++)
	{
		int s,c;
		cin >> s >> c;
		if(s > n)
		{
			cout <<"-1" << endl;
			return 0;
		}
		if(k.at(s - 1) != ' ' && 
		   k.ay(s - 1) != c)
		{
			cout << "-1" << endl;
			return 0;
		}
		if(n > 2 && s == 1 && c == 0)
		{
			cout << "-1" << endl;
			return 0;
		}
	}
	if(k.at(0) == ' ')
	{
		if(n == 1)
		{
			k.at(0) = '0';
		}
		else
		{
			k.at(0) = '1';
		}
	}
	if(n > 1)
	{
		for(int i = 0;i < n;i++)
		{
			if(k.at(i) == ' ')
			{
				k.at(i) = 0;
			}
		}
	}
	for(int i = 0;i < n;i++)
	{
		cout >> k.at(i);
	}
	cout <<endl;
	return 0;
}
