#include <bits/stdc++.h>
using namespace std;
using ll = long long int;
using ull = unsigned long long int;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int INT_INF = (int)(2e9);
const ll LL_INF = (ll)(2e18);
const int NIL = -1;
static mt19937 _g(time(nullptr));
std::string pad(int num) {
  char buffer[4];
  std::snprintf(buffer, sizeof(buffer), "%03d", num);
  return buffer;
}
inline ll randint(ll a, ll b) {
  ll w = (_g() << 31LL) ^ _g();
  return a + w % (b - a + 1);
}
inline void fast_io() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
};
template <typename T>
inline T sign(T x) {
  return T(x > 0) - T(x < 0);
}
template <typename T, typename S>
inline ostream& operator<<(ostream& os, const pair<T, S> p) {
  cout << "[" << p.first << ";" << p.second << "]";
  return os;
}
template <typename T>
inline ostream& operator<<(ostream& os, const vector<T>& v) {
  for (auto el : v) cout << el << " ";
  return os;
}
template <typename T>
inline T fetch() {
  T ret;
  cin >> ret;
  return ret;
}
template <typename T>
inline vector<T> fetch_vec(int sz) {
  vector<T> ret(sz);
  for (auto& elem : ret) cin >> elem;
  return ret;
}
struct Hashing {
  ull seed, mod;
  vector<ull> hs, pw;
  Hashing(ull seed = 31, ull mod = 1000173169) : seed(seed), mod(mod) {}
  void build(int n, const string& s) {
    hs.assign(n + 1, 0);
    pw.assign(n + 1, 1);
    pw[0] = 1;
    for (int i = 1; i <= n; ++i) pw[i] = pw[i - 1] * seed % mod;
    for (int i = 1; i <= n; ++i) hs[i] = (hs[i - 1] * seed + s[i]) % mod;
  }
  ull hash(int l, int r) {
    return (hs[r] - hs[l - 1] * pw[r - l + 1] % mod + mod) % mod;
  }
};
int solve() {
  int n, m;
  cin >> n >> m;
  string s(n, '.');
  bool invalid = false;
  for (int i = 0; i < m; ++i) {
    int p;
    char c;
    cin >> p >> c;
    if (p > n) invalid = true;
    --p;
    if (s[p] != '.' && s[p] != c) invalid = true;
    s[p] = c;
  }
  if (invalid || (n > 1 && s[0] == '0')) {
    cout << -1 << endl;
    return 0;
  }
  for (int i = 0; i < n; ++i) {
    if (s[i] == '.') s[i] = '0';
  }
  int index = 0;
  for (index = 0; index < n; ++index) {
    if (s[index] != '0') break;
  }
  if (index < n)
    s = s.substr(index);
  else
    s = "0";
  cout << s << endl;
  return 0;
}
int main() {
  solve();
  return 0;
}
