#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
using ll = long long;
using P = pair<int, int>;

int main(){
	int n, m;
  	cin >> n >> m;
  	vector<P> p(m);
  	rep(i, m) cin >> p[i].first >> p[i].second;
  	
  	rep(x, 1000){
    	int keta = 1;
      	int nx = x/10;
      	vector<int> d(1, x%10);
      	while(nx){
        	keta++;
          	d.push_back(nx%10);
          	nx /=10;
        }
      	if(keta != n) continue;
      	bool ok = true;
      	reverse(d.begin(), d.end());
      	rep(i, m){
        	if(d[i][p[i].first-1] != p[i].second) ok = false;
        }
      	if(ok){
        	cout << x << endl;
          	return 0;
        }
    }
  
  	cout << -1 << endl;
}