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

int main()
{
	int n, m;
	cin >> n >> m;
	int s[m], c[m];
	for (int i = 0; i < m; ++i)
	{
		cin >> s[i] >> c[i];
	}
	
	for (int i = 0; i < pow(10,n); ++i)
	{
		string str = to_string(i);
		
		if (str.length() != n)
		{
			continue;
		}
		
		bool flag = true;
		
		for (int j = 0; j < m; ++j)
		{
			if (str[s[j]-1] != c[j] + '0')
			{
				flag = false;
				break;
			}
		}
		
		if (flag)
		{
			cout << i << endl;
			return 0;
		}
	}
	
	cout << -1 << endl;
	
	return 0;
}
