#include <bits/stdc++.h>
using namespace std;
using vint = vector<long long>;
using vvint = vector<vint>;
using pint = pair<long long, long long>;
using vpint = vector<pint>;
template <typename T>
using priority_queue_rev = priority_queue<T, vector<T>, greater<T>>;
constexpr long double pi = 3.1415926535897932384626433832795028L;
constexpr long long dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
constexpr long long dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
long long gcd(long long a, long long b) {
  while (b) {
    swap(a %= b, b);
  }
  return a;
}
long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
template <typename T>
void fin(T mes) {
  cout << mes << endl;
  exit(0);
}
template <typename T, typename U>
bool chmax(T &a, const U &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T, typename U>
bool chmin(T &a, const U &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &rhs) {
  os << "(" << rhs.first << ", " << rhs.second << ")";
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
struct setup {
  static constexpr long long PREC = 20;
  setup() {
    cout << fixed << setprecision(PREC);
    cerr << fixed << setprecision(PREC);
  };
} setup;
long long N, M;
long long s[5], c[5];
signed main() {
  cin >> N >> M;
  for (long long i = 0; i < (M); i++) {
    cin >> s[i] >> c[i];
    s[i]--;
  }
  long long st = 1;
  for (long long i = 0; i < (N - 1); i++) {
    st *= 10;
  }
  for (long long i = st; i < st * 10; i++) {
    string x = to_string(i);
    for (long long j = 0; j < (M); j++) {
      if (x.size() <= s[j]) {
        goto nene;
      }
      if (x[s[j]] != c[j] + '0') {
        goto nene;
      }
    }
    fin(x);
  nene:;
  }
  fin(-1);
}
