#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Pi = pair<int, int>;
using Pl = pair<ll, ll>;
using vint = vector<int>;
using vvint = vector<vint>;
using vvvint = vector<vvint>;
using vdouble = vector<double>;
using vvdouble = vector<vdouble>;
using vvvdouble = vector<vvdouble>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using uint = unsigned int;
using ull = unsigned long long;
template <typename T>
using uset = unordered_set<T>;
template <typename T1, typename T2>
using umap = unordered_map<T1, T2>;
constexpr int INF = (1 << 30) - 1;
constexpr ll LLINF = 1LL << 60;
constexpr int dy[] = {1, 0, -1, 0, 1, -1, -1, 1};
constexpr int dx[] = {0, 1, 0, -1, 1, 1, -1, -1};
constexpr char el = '\n';
constexpr int mod = 1000000007;
template <typename T>
T gcd(T a, T b) {
  return (b ? gcd(b, a % b) : a);
}
template <typename T>
T lcm(T a, T b) {
  return (a / gcd(a, b) * b);
}
template <typename T1, typename T2>
inline bool chmin(T1 &a, T2 b) {
  return (a > b && (a = b, true));
}
template <typename T1, typename T2>
inline bool chmax(T1 &a, T2 b) {
  return (a < b && (a = b, true));
}
template <typename T>
ostream &operator<<(ostream &os, vector<T> &v) {
  os << v[0];
  for (int i = 1; i < v.size(); i++) os << " " << v[i];
  return (os);
}
template <typename T>
istream &operator>>(istream &is, vector<T> &v) {
  for (auto &u : v) is >> u;
  return (is);
}
template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  return (is >> p.first >> p.second);
}
void Main() {
  int N, M;
  vint digit(3, -1);
  cin >> N >> M;
  for (int i = 0; i < M; i++) {
    int s, c;
    cin >> s >> c;
    --s;
    if (digit[s] != -1 && c != digit[s]) {
      cout << -1 << endl;
      return;
    }
    digit[s] = c;
  }
  for (int i = 0; i < N - 1; i++) {
    if (digit[i] == 0) {
      cout << -1 << endl;
      return;
    }
  }
  for (int i = 0; i < N; i++) {
    if (digit[i] == -1) {
      cout << 1;
    } else {
      cout << digit[i];
    }
  }
  cout << el;
}
int main() {
  cin.tie(0);
  ios::sync_with_stdio(0);
  cout << fixed << setprecision(20);
  Main();
  return (0);
}
