#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
const ll mod = ll(1e9) + 7;
const ll inf = ll(5e18);
template <typename T1, typename T2>
ll ceill(T1 a, T2 b) {
  return (a + b - 1) / b;
}
void ans(bool b, ostream& out = cout) { out << (b ? "Yes" : "No") << endl; }
void ans2(bool b, ostream& out = cout) { out << (b ? "YES" : "NO") << endl; }
template <typename T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T& val) {
  fill((T*)array, (T*)(array + N), val);
}
int dx[] = {1, 0, -1, 0, 1, -1, 1, -1};
int dy[] = {0, 1, 0, -1, 1, -1, -1, 1};
using namespace std;
namespace dbg {
using ll = long long;
class Debug {
 public:
  Debug() {}
  template <typename T>
  void vd(vector<T> vec);
  template <typename T>
  void vd2(vector<vector<T>> vec);
  template <typename T>
  void ad(T* arr, ll n);
  template <typename T, size_t N>
  void ad2(T (&arr)[N], ll n);
  template <typename T>
  void md(T mp);
};
template <typename T>
void Debug::vd(vector<T> vec) {
  for (auto vv : vec) cout << vv << " ";
  cout << endl;
}
template <typename T>
void Debug::vd2(vector<vector<T>> vec) {
  for (auto vv : vec)
    for (auto vvv : vv) cout << vvv << " ";
  cout << endl;
}
template <typename T>
void Debug::ad(T* arr, ll n) {
  for (int i = 0; i <= n; i++) cout << arr[i] << " ";
  cout << endl;
}
template <typename T, size_t N>
void Debug::ad2(T (&arr)[N], ll n) {
  for (int i = 0; i <= N; i++)
    for (int j = 0; j <= n; j++) cout << arr[i][j] << " ";
  cout << endl;
}
template <typename T>
void Debug::md(T mp) {
  cout << "key : value" << endl;
  for (auto const& m : mp) cout << m.first << " : " << m.second << endl;
  cout << endl;
}
}  // namespace dbg
using dbg::Debug;
Debug debug;
class CGuessTheNumber {
 public:
  void solve(std::istream& in, std::ostream& out) {
    int n, m;
    in >> n >> m;
    vector<int> num(n, -1);
    for (int i = 0; i < m; i++) {
      int s, c;
      in >> s >> c;
      if (num[s - 1] == -1)
        num[s - 1] = c;
      else {
        if (num[s - 1] == c)
          continue;
        else {
          out << -1 << endl;
          return;
        }
      }
    }
    for (int i = 0; i < n; i++) {
      if (num[i] == -1) {
        if (i == 0)
          num[i] = 1;
        else
          num[i] = 0;
      }
    }
    if (num[0] == 0) {
      out << -1 << endl;
      return;
    }
    for (int i = 0; i < n; i++) {
      out << num[i];
    }
    out << endl;
  }
};
int main() {
  CGuessTheNumber solver;
  std::istream& in(std::cin);
  std::ostream& out(std::cout);
  solver.solve(in, out);
  return 0;
}
