#include <bits/stdc++.h>
using namespace std;
struct fast_ios {
  fast_ios() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  };
} fast_ios_;
template <typename T>
istream &operator>>(istream &is, vector<T> &v) {
  for (auto &x : v) is >> x;
  return is;
}
template <typename T>
ostream &operator<<(ostream &os, vector<T> &v) {
  for (long long i = 0; i < v.size(); i++) {
    cout << v[i];
    if (i != v.size() - 1) cout << endl;
  };
  return os;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, pair<T1, T2> p) {
  cout << '(' << p.first << ',' << p.second << ')';
  return os;
}
template <typename T>
void Out(T x) {
  cout << x << endl;
}
template <typename T1, typename T2>
void Ans(bool first, T1 y, T2 n) {
  if (first)
    Out(y);
  else
    Out(n);
}
using vec = vector<long long>;
using mat = vector<vec>;
using Pii = pair<long long, long long>;
using PiP = pair<long long, Pii>;
using PPi = pair<Pii, long long>;
using bools = vector<bool>;
using pairs = vector<Pii>;
const long long mod = 1000000007;
signed main() {
  long long N, M;
  cin >> N >> M;
  vec second(M), c(M);
  for (long long i = (0); i < (M); i++) cin >> second[i] >> c[i];
  string ans(N, '.');
  for (long long i = (0); i < (M); i++) {
    second[i]--;
    if (ans[second[i]] != '.' && ans[second[i]] != '0' + c[i]) {
      {
        cout << (-1) << endl;
        return 0;
      };
    }
    ans[second[i]] = '0' + c[i];
  }
  for (long long i = (0); i < (N); i++)
    if (ans[i] == '.') {
      if (i == 0)
        ans[i] = '1';
      else
        ans[i] = '0';
    }
  if (N == 1) {
    if (ans[0] == '.') ans[0] = '0';
    Out(ans);
    return 0;
  }
  if (ans[0] == '0') {
    {
      cout << (-1) << endl;
      return 0;
    };
  }
  Out(ans);
  return 0;
}
