
	#include <bits/stdc++.h>
	#include <cstdio>
	#include <cstring>
	#include <cmath>
	#include <cstring>
	#include <chrono>
	#include <complex>
	#define endl "\n"
	#define ll long long int
	#define vi vector<int>
	#define vll vector<ll>
	#define vvi vector < vi >
	#define pii pair<int,int>
	#define pll pair<long long, long long>
	#define mod 1000000007
	#define inf 1000000000000000001;
	#define all(c) c.begin(),c.end()
	#define mp(x,y) make_pair(x,y)
	#define mem(a,val) memset(a,val,sizeof(a))
	#define eb emplace_back
	#define f first
	#define s second
	
	using namespace std;
	int main()
	{
		int n,m;
		cin>>n>>m;
		int a[n]={0};
		for(int i=0;i<m;i++)
		{
			int x,y;
			cin>>x>>y;
			a[x-1]=y;
		}
		for(int i=0;i<n;i++)
		{
			if(i==0 && a[i]==0)
			{
				cout<<-1<<endl;
				return 0;
			}
			cout<<a[i];
		}
	}
