#include <bits/stdc++.h>
using namespace std;
using pii = pair<int, int>;
using ll = long long;
using ld = long double;
int ctoi(const char c) {
  if ('0' <= c && c <= '9') return (c - '0');
  return -1;
}
ll gcd(ll a, ll b) { return (b == 0 ? a : gcd(b, a % b)); }
ll lcm(ll a, ll b) { return a * b / gcd(a, b); }
constexpr ll MOD = 1000000007;
constexpr ll INF = 1000000011;
constexpr ll MOD2 = 998244353;
constexpr ll LINF = 1001002003004005006ll;
constexpr ld EPS = 10e-8;
template <class T, class U>
inline bool chmax(T& lhs, const U& rhs) {
  if (lhs < rhs) {
    lhs = rhs;
    return 1;
  }
  return 0;
}
template <class T, class U>
inline bool chmin(T& lhs, const U& rhs) {
  if (lhs > rhs) {
    lhs = rhs;
    return 1;
  }
  return 0;
}
template <typename T>
istream& operator>>(istream& is, vector<T>& v) {
  for (auto&& x : v) is >> x;
  return is;
}
template <typename T, typename U>
istream& operator>>(istream& is, pair<T, U>& p) {
  is >> p.first;
  is >> p.second;
  return is;
}
template <typename T, typename U>
ostream& operator>>(ostream& os, const pair<T, U>& p) {
  os << p.first << ' ' << p.second;
  return os;
}
template <class T>
ostream& operator<<(ostream& os, vector<T>& v) {
  for (auto i = begin(v); i != end(v); ++i) {
    if (i != begin(v)) os << ' ';
    os << *i;
  }
  return os;
}
ll A[5];
int main() {
  ll N, M;
  cin >> N >> M;
  if (M == 0) {
    cout << (N == 1 ? 0 : pow(10, N)) << '\n';
    return 0;
  }
  for (ll i = 0; i < (5); ++i) {
    A[i] = INF;
  }
  for (ll i = 0; i < (M); ++i) {
    ll X, K;
    cin >> X >> K;
    X--;
    if (A[X] == INF) {
      A[X] = K;
    } else if (A[X] != K) {
      cout << -1 << '\n';
      return 0;
    }
  }
  if (A[0] == 0 && N == 1) {
    cout << 0 << '\n';
    return 0;
  }
  if (A[0] == 0 && N != 1) {
    cout << -1 << '\n';
    return 0;
  }
  for (ll i = 0; i < (N); ++i) {
    cout << (A[i] != INF ? A[i] : (i == 0 ? 1 : 0));
  }
  cout << '\n';
}
