#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
const int MOD = 1e9 + 7;
const ll INF = 1LL << 60;
const int inf = 1 << 25;
constexpr long double pi = 3.141592653589793238462643383279;
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
ll fact(ll i) {
  if (i == 0) return 1;
  return ((fact(i - 1)) * i) % MOD;
}
ll gcd(ll a, ll b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) { return a * b / gcd(a, b); }
ll keta(ll n) {
  if (n == 0) return 1;
  ll count = 0;
  while (n != 0) {
    n /= 10;
    count++;
  }
  return count;
}
ll ketasum(ll n) {
  ll sum = 0;
  while (n != 0) {
    sum += n % 10;
    n /= 10;
  }
  return sum;
}
ll mch(ll n) {
  if (n == 1)
    return 1;
  else
    return n * mch(n - 1);
}
ll modpow(ll a, ll n, ll mod) {
  ll hi = 1;
  while (n > 0) {
    if (n & 1) hi = hi * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return hi;
}
bool is_prime(const unsigned n) {
  switch (n) {
    case 0:
    case 1:
      return false;
    case 2:
    case 3:
      return true;
  }
  if (n % 2 == 0 || n % 3 == 0) return false;
  for (unsigned i = 5; i * i <= n; i += 6) {
    if (n % i == 0) return false;
    if (n % (i + 2) == 0) return false;
  }
  return true;
}
int main(void) {
  bool flag = true;
  int n, m;
  cin >> n >> m;
  vector<pair<int, int>> p(m);
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    --b;
    p[i] = make_pair(a, b);
  }
  for (int i = 0; i < 1000; i++) {
    string s = to_string(i);
    if (s.size() == n) {
      for (int j = 0; j < m; j++) {
        if ((s[p[j].first] - '0') != p[j].second) {
          flag = false;
        }
      }
      if (flag) {
        cout << i << "\n";
        return 0;
      }
    }
  }
  cout << -1 << "\n";
  return 0;
}
