#include <bits/stdc++.h>
using namespace std;
using namespace std::chrono;
template <typename A>
ostream &operator<<(ostream &cout, vector<A> const &v);
template <typename A, typename B>
ostream &operator<<(ostream &cout, pair<A, B> const &p) {
  return cout << "(" << p.first << ", " << p.second << ")";
}
template <typename A>
ostream &operator<<(ostream &cout, vector<A> const &v) {
  cout << "[";
  for (int i = 0; i < v.size(); i++) {
    if (i) cout << ", ";
    cout << v[i];
  }
  return cout << "]";
}
template <typename A, typename B>
istream &operator>>(istream &cin, pair<A, B> &p) {
  cin >> p.first;
  return cin >> p.second;
}
mt19937 rng(61378913);
void usaco(string filename) {
  freopen((filename + ".in").c_str(), "r", stdin);
  freopen((filename + ".out").c_str(), "w", stdout);
}
const long double pi = 3.14159265358979323846;
long long n, m, k, q, l, r, x, y, z;
long long a[1000005];
long long b[1000005];
long long c[1000005];
string second, t;
long long ans = 0;
void solve(int tc) {
  cin >> n >> m;
  second = string(3, '0');
  bool sx[3] = {0};
  bool pos = 1;
  for (long long i = 0; i < (m); ++i) {
    cin >> x >> y;
    --x;
    if (sx[x] && second[x] != '0' + y) {
      cout << -1 << '\n';
      return;
    }
    sx[x] = 1;
    second[x] = '0' + y;
  }
  bool first = 0;
  for (long long i = 0; i < (n - 1); ++i) {
    if (second[i] > '0') first = 1;
    if (!first && sx[i]) {
      cout << -1 << '\n';
      return;
    }
    if (first) cout << second[i];
  }
  cout << second[n - 1] << '\n';
}
int main() {
  { ios_base::sync_with_stdio(false); }
  {
    cin.tie(NULL);
    cout.tie(NULL);
  }
  int tc = 1;
  for (int t = 0; t < tc; t++) solve(t);
}
