#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp> 
#include <ext/pb_ds/tree_policy.hpp> 
using namespace __gnu_pbds;
using namespace std;
typedef tree<pair<int,int>,null_type,less<pair<int,int>>,rb_tree_tag,tree_order_statistics_node_update> oset;
#define sim template < class c
#define ris return * this
#define dor > debug & operator <<
#define eni(x) sim > typename \
  enable_if<sizeof dud<c>(0) x 1, debug&>::type operator<<(c i) {
sim > struct rge { c b, e; };
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c* x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
~debug() { cerr << endl; }
eni(!=) cerr << boolalpha << i; ris; }
eni(==) ris << range(begin(i), end(i)); }
sim, class b dor(pair < b, c > d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
	*this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
sim dor(const c&) { ris; }
#endif
};
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
using ll = long long;

void test_case(){
	int n , m; cin >> n >> m;
	if(n==1 && m==0){
		cout<<0;
		return;
	}
	int s , c;
	vector<int> hash(n,0);
	vector<int> arr(n,0);
	for(int i = 0 ; i < m ; i++){
		cin >> s >> c;
		s--;
		if(hash[s] != 0 && arr[s] != c){
			cout<<"-1\n";
			return;
		}
		hash[s] = 1;
		arr[s] = c;
	}
	string res = "";
	if(hash[0] == 0){
		arr[0] = 1;
	}
	for(int i = 0 ; i < n ; i++){
		res += arr[i]-'0';
	}
	if((int)res.size() != n || (res[0]=='0' && n!=1)){
		cout<<"-1\n";
		return;
	}
	cout<<res;
}
 
int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);
	int T=1;
	//~ cin >> T;
	while(T--){
		test_case();
	}
	return 0;
}
