#include <bits/stdc++.h>
using namespace std;
const int mod = 1000000007;
struct mint {
  long long x;
  mint(long long x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint& operator+=(const mint a) {
    if ((x += a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator-=(const mint a) {
    if ((x += mod - a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }
  mint pow(long long t) const {
    if (!t) return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1) a *= *this;
    return a;
  }
  mint inv() const { return pow(mod - 2); }
  mint& operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream& operator>>(istream& is, mint& a) { return is >> a.x; }
ostream& operator<<(ostream& os, const mint& a) { return os << a.x; }
int main() {
  int n, m;
  cin >> n >> m;
  int ans = 0;
  vector<int> a(n, -1);
  for (int i = 0; i < (m); i++) {
    int s, c;
    cin >> s >> c;
    if (a.at(s - 1) == -1)
      a.at(s - 1) = c;
    else {
      if (a.at(s - 1) != c) {
        cout << "-1" << endl;
        return 0;
      }
    }
  }
  if (n == 2 || n == 3) {
    if (a.at(0) == 0) {
      cout << "-1" << endl;
      return 0;
    }
  }
  for (int i = 0; i < (3); i++) {
    if (a.at(i) == -1 && i == 0)
      cout << 1;
    else if (a.at(i) == -1)
      cout << 0;
    else
      cout << a.at(i);
  }
  cout << endl;
  return 0;
}
