#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<ll, ll>;
using vl = vector<ll>;
using vvl = vector<vl>;
ll gcd(ll a, ll b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
const ll MOD = 1000000007;
const ll MAX = 2000001;
ll mod(ll a) { return a % MOD; }
ll lcm(ll a, ll b) { return (a * b) / gcd(a, b); }
ll fac[MAX], finv[MAX], inv[MAX];
void nCrprep() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (ll i = 2; i < MAX; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}
ll nCr(ll n, ll r) {
  if (n < r) return 0;
  if (n < 0 || r < 0) return 0;
  return fac[n] * (finv[r] * finv[n - r] % MOD) % MOD;
}
ll nCrcheep(ll n, ll r) {
  if (r == 0)
    return 1;
  else if (r == 1)
    return n;
  else
    return nCrcheep(n - 1, r - 1) * n / r;
}
vector<pair<ll, ll>> prime_factorize(ll n) {
  vector<pair<ll, ll>> res;
  for (ll i = 2; i * i <= n; i++) {
    if (n % i != 0) continue;
    ll ex = 0;
    while (n % i == 0) {
      ex++;
      n /= i;
    }
    res.push_back({i, ex});
  }
  if (n != 1) res.push_back({n, 1});
  return res;
}
int main() {
  ll n, m;
  cin >> n >> m;
  ll ans = -1;
  set<pair<ll, ll>> con;
  for (int i = 0; i < (m); i++) {
    ll a, b;
    cin >> a >> b;
    con.insert(make_pair(a, b));
  }
  for (ll i = pow(10, n - 1); i < pow(10, n); i++) {
    bool flag = true;
    ll id = i;
    vl num(n);
    for (int i = 0; i < (n); i++) {
      num[i] = id % 10;
      id /= 10;
    }
    for (auto p : con) {
      ll a = p.first;
      ll b = p.second;
      if (num[n - a] != b) {
        flag = false;
        break;
      }
    }
    if (n == 1) {
      for (auto p : con) {
        if (p.first == 1 and p.second == 0) ans = 0;
      }
    }
    if (flag) {
      ans = i;
      break;
    }
  }
  cout << ans << endl;
}
