#include <bits/stdc++.h>
using namespace std;
void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(char x) { cerr << '\'' << x << '\''; }
void __print(const char *x) { cerr << '\"' << x << '\"'; }
void __print(const string &x) { cerr << '\"' << x << '\"'; }
void __print(bool x) { cerr << (x ? "true" : "false"); }
template <typename T, typename V>
void __print(const pair<T, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename T>
void __print(const T &x) {
  int f = 0;
  cerr << '{';
  for (auto &i : x) cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\n"; }
template <typename T, typename... V>
void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v)) cerr << ", ";
  _print(v...);
}
mt19937_64 rnd;
const int N = 2e5 + 5;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  vector<pair<int, int> > cond;
  for (int i = 0; i < m; i++) {
    int x, y;
    cin >> x >> y;
    cond.push_back(make_pair(x - 1, y));
  }
  for (int i = 1; i <= 999; i++) {
    function<bool(int)> check = [&](int n) {
      vector<int> res;
      while (n > 0) {
        res.push_back(n % 10);
        n /= 10;
      }
      reverse((res).begin(), (res).end());
      bool ok = true;
      for (auto &x : cond) {
        ok &= (res[x.first] == x.second);
      }
      return ok;
    };
    if (check(i)) {
      cout << i;
      return 0;
    }
  }
  cout << -1;
  return 0;
}
