#include <bits/stdc++.h>
using namespace std;
template <unsigned int MD>
struct ModInt {
  using M = ModInt;
  const static M G;
  unsigned int v;
  ModInt(long long _v = 0) { set_v(unsigned int(_v % MD + MD)); }
  M& set_v(unsigned int _v) {
    v = (_v < MD) ? _v : _v - MD;
    return *this;
  }
  explicit operator bool() const { return v != 0; }
  M operator-() const { return M() - *this; }
  M operator+(const M& r) const { return M().set_v(v + r.v); }
  M operator-(const M& r) const { return M().set_v(v + MD - r.v); }
  M operator*(const M& r) const {
    return M().set_v(unsigned int(unsigned long long(v) * r.v % MD));
  }
  M operator/(const M& r) const { return *this * r.inv(); }
  M& operator+=(const M& r) { return *this = *this + r; }
  M& operator-=(const M& r) { return *this = *this - r; }
  M& operator*=(const M& r) { return *this = *this * r; }
  M& operator/=(const M& r) { return *this = *this / r; }
  bool operator==(const M& r) const { return v == r.v; }
  M pow(long long n) const {
    M x = *this, r = 1;
    while (n) {
      if (n & 1) r *= x;
      x *= x;
      n >>= 1;
    }
    return r;
  }
  M inv() const { return pow(MD - 2); }
  friend ostream& operator<<(ostream& os, const M& r) { return os << r.v; }
};
using Mint = ModInt<1000000007>;
const double PI = 3.14159265358979323846;
bool compare_by_b(pair<int, int> a, pair<int, int> b) {
  if (a.second != b.second) {
    return a.second < b.second;
  } else {
    return a.first < b.first;
  }
}
bool is_prime(long long N) {
  if (N == 1) return false;
  for (long long i = 2; i * i <= N; ++i) {
    if (N % i == 0) return false;
  }
  return true;
}
int main() {
  int n, m;
  cin >> n >> m;
  vector<pair<int, int>> p(m);
  for (long long i = (long long)0; i < (long long)m; i++) {
    int a, b;
    cin >> a >> b;
    p[i] = make_pair(a, b);
  }
  int ans = -1;
  for (long long i = (long long)0; i < (long long)1000; i++) {
    string s = to_string(i);
    bool ok[3] = {true, true, true};
    for (long long j = (long long)0; j < (long long)m; j++) {
      if (i <= 9) {
        if (p[j].first == 1) {
          if (s[0] - '0' != p[j].second) {
            ok[0] = false;
            break;
          }
        } else {
          ok[0] = false;
          break;
        }
      } else if (10 <= i && i < 100) {
        if (p[j].first == 1) {
          if (s[0] - '0' != p[j].second) {
            ok[0] = false;
            break;
          }
        } else if (p[j].first == 2) {
          if (s[1] - '1' != p[j].second) {
            ok[1] = false;
            break;
          }
        } else {
          ok[1] = false;
          break;
        }
      } else {
        if (p[j].first == 1) {
          if (s[0] - '0' != p[j].second) {
            ok[0] = false;
            break;
          }
        } else if (p[j].first == 2) {
          if (s[1] - '1' != p[j].second) {
            ok[1] = false;
            break;
          }
        } else if (p[j].first == 3) {
          if (s[2] - '0' != p[j].second) {
            ok[2] = false;
            break;
          }
        }
      }
    }
    if (ok[0] && ok[1] && ok[2] && s.length() == n) {
      ans = i;
      break;
    }
  }
  cout << ans << endl;
}
