#include <bits/stdc++.h>
using namespace std;
const int inf = 1e9 + 7;
const long long INF = 1e18;
template <typename T1, typename T2>
inline bool chmin(T1& a, T2 b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T1, typename T2>
inline bool chmax(T1& a, T2 b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T>
T gcd(T a, T b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
template <typename T>
T lcm(T a, T b) {
  return a / gcd(a, b) * b;
}
template <typename T>
T pow(T a, int b) {
  return b ? pow(a * a, b / 2) * (b % 2 ? a : 1) : 1;
}
const int mod = 1000000007;
long long modpow(long long a, int b) {
  return b ? modpow(a * a % mod, b / 2) * (b % 2 ? a : 1) % mod : 1;
}
template <class T>
ostream& operator<<(ostream& os, const vector<T>& vec) {
  for (int i = 0; i < ((int)vec.size()); ++i) {
    if (i) os << " ";
    os << vec[i];
  }
  return os;
}
template <class T, class U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
  os << p.first << " " << p.second;
  return os;
}
template <class T>
inline void add(T& a, int b) {
  a += b;
  if (a >= mod) a -= mod;
}
void solve();
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout << fixed << setprecision(10);
  int T;
  T = 1;
  while (T--) {
    solve();
  }
}
void solve() {
  int n, m;
  cin >> n >> m;
  vector<pair<int, int> > v(m);
  for (int i = 0; i < (m); ++i) {
    int s, c;
    cin >> s >> c;
    s--;
    v[i] = pair<int, int>(s, c);
  }
  sort(v.begin(), v.end());
  v.erase(unique(v.begin(), v.end()), v.end());
  m = (int)v.size();
  for (int i = 0; i < (m - 1); ++i) {
    if (v[i].first == v[i + 1].first && v[i].second != v[i + 1].second) {
      cout << -1 << endl;
      return;
    }
  }
  vector<int> tmp(n, 1);
  for (int i = 0; i < (m); ++i) tmp[v[i].first] = v[i].second;
  if (n == 1 && (int)tmp.size() == 0) {
    cout << 0 << endl;
    return;
  }
  if (n == 1) {
    cout << tmp[0] << endl;
    return;
  }
  if (n == 2 && tmp[0] == 0 && tmp[1] == 0) {
    cout << 0 << endl;
    return;
  }
  if (n == 2 && tmp[0] == 0) {
    cout << -1 << endl;
    return;
  }
  if (n == 3 && tmp[0] == 0 && tmp[1] == 0 && tmp[2] == 0) {
    cout << 0 << endl;
    return;
  }
  if (n == 3 && (tmp[0] == 0 || (tmp[0] == 0 && tmp[1] == 0))) {
    cout << -1 << endl;
    return;
  }
  vector<int> x(n);
  for (int i = 0; i < (m); ++i) x[v[i].first] = v[i].second;
  if (x[0] == 0) x[0] = 1;
  for (int i = 0; i < (n); ++i) cout << x[i];
  cout << endl;
}
