#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B>
ostream& operator<<(ostream& out, const pair<A, B>& a) {
  out << "(" << a.first << "," << a.second << ")";
  return out;
}
template <typename T, size_t N>
ostream& operator<<(ostream& out, const array<T, N>& a) {
  out << "[";
  bool first = true;
  for (auto& v : a) {
    out << (first ? "" : ", ");
    out << v;
    first = 0;
  }
  out << "]";
  return out;
}
template <typename T>
ostream& operator<<(ostream& out, const vector<T>& a) {
  out << "[";
  bool first = true;
  for (auto& v : a) {
    out << (first ? "" : ", ");
    out << v;
    first = 0;
  }
  out << "]";
  return out;
}
template <typename T, class Cmp>
ostream& operator<<(ostream& out, const set<T, Cmp>& a) {
  out << "{";
  bool first = true;
  for (auto& v : a) {
    out << (first ? "" : ", ");
    out << v;
    first = 0;
  }
  out << "}";
  return out;
}
template <typename U, typename T, class Cmp>
ostream& operator<<(ostream& out, const map<U, T, Cmp>& a) {
  out << "{";
  bool first = true;
  for (auto& p : a) {
    out << (first ? "" : ", ");
    out << p.first << ":" << p.second;
    first = 0;
  }
  out << "}";
  return out;
}
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  cerr << name << ": " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << ": " << arg1 << " |";
  __f(comma + 1, args...);
}
const int INF = 1 << 29;
const int MOD = 1e9 + 7;
mt19937 mrand(random_device{}());
int rnd(int x) { return mrand() % x; }
struct fast_ios {
  fast_ios() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
  };
} fast_ios_;
int main() {
  int n, m;
  cin >> n >> m;
  vector<int> ret(n, -1);
  bool found = false;
  while (m--) {
    int x, y;
    cin >> x >> y;
    --x;
    if (ret[x] < 0) {
      ret[x] = y;
    } else {
      if (ret[x] != y) found = true;
    }
  }
  if (found || (n > 1 && ret[0] == 0)) {
    cout << -1 << endl;
    return 0;
  }
  for (int i = 0; i < n; ++i) {
    if (ret[i] < 0) {
      cout << (i == 0 ? 1 : 0);
    } else {
      cout << ret[i];
    }
  }
  cout << endl;
  return 0;
}
