#include <bits/stdc++.h>
const int MOD = 1e9 + 7;
const int iINF = 2147483647 / 2;
const long long int llINF = 9223372036854775807 / 2;
using namespace std;
using ll = long long int;
using vl = vector<ll>;
using vvl = vector<vector<ll>>;
using vvvl = vector<vector<vector<ll>>>;
bool paircomp(const pair<ll, ll> &a, const pair<ll, ll> &b) {
  if (a.first == b.first) return a.second < b.second;
  return a.first < b.first;
}
ll POW(ll n, ll m) {
  if (m == 0) {
    return 1;
  } else if (m % 2 == 0) {
    ll tmp = POW(n, m / 2);
    return (tmp * tmp);
  } else {
    return (n * POW(n, m - 1));
  }
}
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ll N, M;
  cin >> N >> M;
  vl A(N, -1);
  for (ll i = 0; i < (M); i++) {
    ll s, c;
    cin >> s >> c;
    if (A[s - 1] != -1 && A[s - 1] != c) {
      cout << -1 << endl;
      return 0;
    }
    A[s - 1] = c;
  }
  if (A[0] == 0 && N > 1) {
    cout << -1 << endl;
    return 0;
  }
  ll ans = 0;
  for (ll i = 0; i < (N); i++) {
    if (A[i] == -1 && i == 0) {
      ans += POW(10, N - 1 - i);
    } else if (A[i] != -1)
      ans += A[i] * POW(10, N - 1 - i);
  }
  cout << ans << endl;
  return 0;
}
