#include<iostream>
using namespace std;

int n,m,s[9],c[9],d[9],ans;
bool ok[9];

int main()
{
	cin >> n >> m;
	for(int i = 1;i<=m;i++)
	{
		cin >> s[i] >> c[i];
		if(ok[s[i]] and c[i]!=d[s[i]])
		{
			cout << -1;
			return 0;
		}
		if(s[i]==1 and c[i]==0 and n!=1)
		{
			cout << -1;
			return 0;
		}
		d[s[i]] = c[i];
		ok[s[i]] = 1;
	}
	if(ok[1]==0 and n!=1)d[1] = 1;
	if(n==1)cout << d[1];
	if(n==2)cout << d[2]+d[1]*10;
	if(n==3)cout << d[3]+d[2]*10+d[1]*100;
	return 0;
}