#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using db = double;
using ld = long double;
template <typename T>
using V = vector<T>;
template <typename T>
using VV = vector<vector<T>>;
const ll mod = 1000000007;
const ll INF = 1000000099;
const ll LINF = (ll)(1e18 + 99);
const vector<ll> dx = {-1, 1, 0, 0}, dy = {0, 0, -1, 1};
template <typename T, typename U>
inline bool chmin(T& t, const U& u) {
  if (t > u) {
    t = u;
    return 1;
  }
  return 0;
}
template <typename T, typename U>
inline bool chmax(T& t, const U& u) {
  if (t < u) {
    t = u;
    return 1;
  }
  return 0;
}
template <typename T>
inline T gcd(T a, T b) {
  return b ? gcd(b, a % b) : a;
}
template <typename T, typename Y>
inline T mpow(T a, Y n) {
  T res = 1;
  for (; n; n >>= 1) {
    if (n & 1) res = res * a;
    a = a * a;
  }
  return res;
}
signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(20);
  int n, m;
  cin >> n >> m;
  V<int> s(m), c(m);
  for (ll i = 0; i < (ll)(m); ++i) {
    cin >> s[i] >> c[i];
    s[i] = n - s[i];
  }
  for (ll i = mpow(10, n - 1); i < (ll)(mpow(10, n)); ++i) {
    bool ok = true;
    for (ll j = 0; j < (ll)(m); ++j) {
      if ((i / mpow(10, s[j])) % 10 != c[j]) ok = false;
      ;
    }
    if (ok) {
      cout << i << '\n';
      return 0;
    }
  }
  cout << -1 << '\n';
}
