#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using unit = unsigned;
using vl = vector<ll>;
using ull = unsigned long long;
using vvi = vector<vi>;
using vvl = vector<vl>;
using pii = pair<int, int>;
using vpii = vector<pii>;
using pil = pair<int, ll>;
using vpil = vector<pil>;
using pli = pair<ll, int>;
using vpli = vector<pli>;
using pll = pair<ll, ll>;
using vpll = vector<pll>;
void _main();
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  _main();
}
template <class T>
string join(const vector<T> &v) {
  stringstream s;
  for (int(i) = (int)(0); (i) < (int)(((long long)(v).size())); ++(i))
    s << ' ' << v[i];
  return s.str().substr(1);
}
template <class T>
istream &operator>>(istream &i, vector<T> &v) {
  for (auto &x : v) {
    i >> v;
  }
  return i;
}
template <class T>
ostream &operator<<(ostream &o, const vector<T> &v) {
  o << "[";
  for (auto &x : v) o << x << ",";
  o << "]";
  return o;
}
template <class T>
ostream &operator<<(ostream &o, const deque<T> &v) {
  o << "deq[";
  for (auto &x : v) o << x << ",";
  o << "]";
  return o;
}
template <class T>
ostream &operator<<(ostream &o, const set<T> &v) {
  o << "{";
  for (auto &x : v) o << x << ",";
  o << "}";
  return o;
}
template <class T>
ostream &operator<<(ostream &o, const unordered_set<T> &v) {
  o << "{";
  for (auto &x : v) o << x << ",";
  o << "}";
  return o;
}
template <class T>
ostream &operator<<(ostream &o, const multiset<T> &v) {
  o << "{";
  for (auto &x : v) o << x << ",";
  o << "}";
  return o;
}
template <class T>
ostream &operator<<(ostream &o, const unordered_multiset<T> &v) {
  o << "{";
  for (auto &x : v) o << x << ",";
  o << "}";
  return o;
}
template <class T1, class T2>
ostream &operator<<(ostream &o, const pair<T1, T2> &p) {
  o << "(" << p.first << "," << p.second << ")";
  return o;
}
template <class TK, class TV>
ostream &operator<<(ostream &o, const map<TK, TV> &m) {
  o << "{";
  for (auto &x : m) o << x.first << "=>" << x.second << ",";
  o << "}";
  return o;
}
template <class TK, class TV>
ostream &operator<<(ostream &o, const unordered_map<TK, TV> &m) {
  o << "{";
  for (auto &x : m) o << x.first << "=>" << x.second << ",";
  o << "}";
  return o;
}
template <class T>
void YES(T c) {
  if (c)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
template <class T>
void Yes(T c) {
  if (c)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}
template <class T>
void POSS(T c) {
  if (c)
    cout << "POSSIBLE" << endl;
  else
    cout << "IMPOSSIBLE" << endl;
}
template <class T>
void Poss(T c) {
  if (c)
    cout << "Possible" << endl;
  else
    cout << "Impossible" << endl;
}
template <class T>
bool chmax(T &a, const T &b) {
  return a < b ? (a = b, true) : false;
}
template <class T>
bool chmin(T &a, const T &b) {
  return a > b ? (a = b, true) : false;
}
template <class T>
T gcd(T a, T b) {
  return b ? gcd(b, a % b) : a;
}
template <class T>
T lcm(T a, T b) {
  return a / gcd(a, b) * b;
}
const double EPS = 1e-10;
const double PI = acos(-1.0);
const int INF = 1001002003;
const ll LINF = 1001002003004005006LL;
const int DX[] = {-1, 0, 1, 0, -1, -1, 1, 1};
const int DY[] = {0, 1, 0, -1, -1, 1, -1, 1};
void ng() {
  cout << -1 << endl;
  exit(0);
}
void _main() {
  int n, m;
  cin >> n >> m;
  vi s(m), c(m);
  for (int(i) = (int)(0); (i) < (int)(m); ++(i)) cin >> s[i] >> c[i];
  vi a(n, -1);
  for (int(i) = (int)(0); (i) < (int)(m); ++(i)) {
    int si = s[i] - 1, ci = c[i];
    if (si == 0 && ci == 0) ng();
    if (a[si] != -1 && a[si] != ci) ng();
    a[si] = ci;
  }
  chmax(a[0], 1);
  for (int(i) = (int)(1); (i) < (int)(n); ++(i)) chmax(a[i], 0);
  for (auto &x : a) cout << x;
  cout << endl;
}
