#include <bits/stdc++.h>
using namespace std;

// boost
#include <boost/multiprecision/cpp_int.hpp>
using boost::multiprecision::cpp_int;

using ll = long long;
using ld = long double;

using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vb = vector<bool>;
using vs = vector<string>;
using vld = vector<ld>;
using vvld = vector<vld>;

typedef pair<ll, ll> P;

#define bit(n) (1LL << (n))

//#define int long long

#define all(v) v.begin(), v.end()

#define rep(i, n) for (ll i = 0; i < n; i++)
#define REP(i, n) for (ll i = 1; i < n; i++)

#define FOR(i, a, b) for (ll i = (a); i < (b); i++)
#define FORm(i, m) for (auto i = m.begin(); i != m.end(); i++)

template <class T>
inline void chmax(T& a, T b) {
  a = std::max(a, b);
}
template <class T>
inline void chmin(T& a, T b) {
  a = std::min(a, b);
}

#define mod (ll)(1e9 + 7)
// #define mod (998244353ll)

const long long INF = 1LL << 60;

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(20);

  ll n, m;
  cin >> n >> m;

  vector<P> a(m);
  rep(i, m) {
    cin >> a[i].first >> a[i].second;
  }

  ll s = pow(10, n - 1);
  ll e = s * 10;

  FOR(i, s, e) {
    bool ok = true;
    for (auto [s, c] : a) {
      ll v = (i / (int)pow(10, n - s)) % 10;
      if (v != c) {
        ok = false;
      }
    }
    if (ok) {
      cout << i << endl;
      return 0;
    }
  }

  cout << -1 << endl;

  return 0;
}
