#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define ll long long 
#define REP(i, a, b) for (ll i = a; i < b; i++)
#define REPI(i, a, b) for (ll i = b - 1; i >= a; i--)
#define i_os ios::sync_with_stdio(0);  cin.tie(0);  cout.tie(0);
#define INF (ll)1e18 + 100
#define endl "\n"
#define p0(a) cout << a << " "
#define p1(a) cout << a << endl
#define p2(a, b) cout << a << " " << b << endl
#define p3(a, b, c) cout << a << " " << b << " " << c << endl
#define p4(a, b, c, d) cout << a << " " << b << " " << c << " " << d << endl
#define MAX 1e6
/*SOME BITMASK KNOWLEDGE
1)x & (x - 1):sets the last one bit of x to zero
power of two exactly when x & (x − 1) = 0.
2)x & -x:sets all the one bits to zero, except last one bit
3)x | (x - 1):inverts all the bits after the last one bit*/
#define o_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>
#define o_setll tree<ll, null_type, less<ll>, rb_tree_tag, tree_order_statistics_node_update>
typedef tree<pair<ll, ll>,null_type,less<pair<ll, ll>>,rb_tree_tag,tree_order_statistics_node_update> indexed_set;
//1. order_of_key(k) : number of elements strictly lesser than k
//2. find_by_order(k) : k-th element in the set

int main() 
{
	ll n,m;
	cin>>n>>m;
	string s = "";
	REP(i,0,n) s.push_back('0');

	unordered_map<ll,ll> um;
	REP(i,0,m){
		ll x,y;
		cin>>x>>y;
		if(um.count(x) && um[x] != y){
			cout<<-1<<endl;
			return 0;
		}
		if(x == 1 && y == 0 && n > 1){
			cout<<-1<<endl;
			return 0;
		}
		s[x-1] = y + '0';
		um[x] = y;
	}
	if(s[0] == '0') s[0] = '1';
	cout<<s<<endl;
	return 0;
}

