#include <bits/stdc++.h>
using ll = long long;
const ll MOD = 998244353;
const int INF = (ll)1e9 + 7;
const ll INFLL = (ll)1e18;
using namespace std;
template <class t>
using vvector = vector<vector<t>>;
template <class t>
using vvvector = vector<vector<vector<t>>>;
template <class t>
using priority_queuer = priority_queue<t, vector<t>, greater<t>>;
template <class t, class u>
bool chmax(t &a, u b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class t, class u>
bool chmin(t &a, u b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
ll modpow(ll x, ll b) {
  ll res = 1;
  while (b) {
    if (b & 1) res = res * x % MOD;
    x = x * x % MOD;
    b >>= 1;
  }
  return res;
}
ll modinv(ll x) { return modpow(x, MOD - 2); }
bool was_output = false;
template <class t>
void output(t a) {
  if (was_output) cout << " ";
  cout << a;
  was_output = true;
}
void outendl() {
  was_output = false;
  cout << endl;
}
ll in() {
  ll res;
  scanf("%lld", &res);
  return res;
}
template <class t>
istream &operator>>(istream &is, vector<t> &x) {
  for (auto &i : x) is >> i;
  return is;
}
template <class t, class u>
istream &operator>>(istream &is, pair<t, u> &x) {
  is >> x.first >> x.second;
  return is;
}
template <class t>
void in(t &x) {
  cin >> x;
}
template <class t>
void out(t x) {
  cout << x;
}
int main() {
  int n = in();
  int m = in();
  vector<pair<int, char>> order(m);
  for (auto &i : (order)) {
    i.first = in() - 1;
    in(i.second);
  }
  string ans = "-1";
  for (int i = (modpow(10, n - 1)) * (strlen("modpow(10, n)") != 0);
       i < (int)(strlen("modpow(10, n)") ? modpow(10, n) : (modpow(10, n - 1)));
       ++i) {
    string str = to_string(i);
    bool flag = true;
    for (auto &j : (order)) {
      if (str[j.first] != j.second) {
        flag = false;
        break;
      }
    }
    if (flag) {
      ans = str;
      break;
    }
  }
  cout << ans << endl;
  return 0;
}
