#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vs = vector<string>;
using vpll = vector<pair<ll, ll>>;
using vtp = vector<tuple<ll, ll, ll>>;
using vb = vector<bool>;
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
const ll INF = 1e9 + 10;
const ll MOD = 1e9 + 7;
const ll LINF = 1e18;
signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll n, m;
  cin >> n >> m;
  vll a(n, -1);
  for (long long i = (long long)(0); i < (long long)(m); ++i) {
    ll s, c;
    cin >> s >> c;
    s--;
    if (a[s] == -1) {
      a[s] = c;
    } else if (a[s] != c) {
      cout << -1 << endl;
      return 0;
    }
  }
  if (n == 1) {
    if (a[0] == 0 || a[0] == -1)
      cout << -1 << endl;
    else
      cout << a[0] << endl;
  } else {
    if (a[0] == 0) {
      cout << -1 << endl;
      return 0;
    }
    if (a[0] == -1) a[0] = 1;
    for (long long i = (long long)(0); i < (long long)(n); ++i)
      if (a[i] == -1) a[i] = 0;
    for (long long i = (long long)(0); i < (long long)(n); ++i) cout << a[i];
    cout << endl;
  }
}
