#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...);
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int N, M;
  cin >> N >> M;
  vector<pair<int, char>> sc(M);
  for (int i = 0; i < (int)(M); i++) {
    cin >> sc[i].first >> sc[i].second;
  }
  for (int i = pow(10, N - 1); i < pow(10, N); i++) {
    string cand = to_string(i);
    int not_good = 0;
    for (int j = 0; j < (int)(M); j++) {
      if (cand[sc[j].first - 1] != sc[j].second) {
        not_good++;
      }
    }
    if (not_good == 0) {
      cout << cand << endl;
      return 0;
    }
  }
  cout << -1 << endl;
  return 0;
}
