#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using vll = vector<ll>;
using vvll = vector<vll>;
using pll = pair<ll, ll>;
using vpll = vector<pll>;
using vvpll = vector<vpll>;
using tll = tuple<ll, ll, ll>;
using vtll = vector<tll>;
using vvtll = vector<vtll>;
template <typename Head>
void dump_1(const char* str, Head&& h) {
  cerr << str << ": " << h << '\n';
}
template <typename Head, typename... Tail>
void dump_1(const char* str, Head&& h, Tail&&... t) {
  while (*str != ',') {
    cerr << *str++;
  }
  cerr << ": " << h << ' ';
  dump_1(str + 1, t...);
}
template <typename T>
void dumpa_1(const char* str, const T v[], const ll size) {
  while (*str != ',') {
    cerr << *str++;
  }
  cerr << ": ";
  for (ll i = 0; i < (size); i++) {
    if (i != 0) {
      cerr << ' ';
    }
    cerr << v[i];
  }
  cerr << '\n';
}
template <typename T1, typename T2>
ostream& operator<<(ostream& os, const pair<T1, T2>& v) {
  os << v.first << ' ' << v.second;
  return os;
}
template <typename T1, typename T2, typename T3>
ostream& operator<<(ostream& os, const tuple<T1, T2, T3>& v) {
  os << get<0>(v) << ' ' << get<1>(v) << ' ' << get<2>(v);
  return os;
}
template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) {
      os << ' ';
    }
    os << *it;
  }
  return os;
}
template <typename T>
ostream& operator<<(ostream& os, const set<T>& v) {
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) {
      os << ' ';
    }
    os << *it;
  }
  return os;
}
template <typename T>
ostream& operator<<(ostream& os, const multiset<T>& v) {
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) {
      os << ' ';
    }
    os << *it;
  }
  return os;
}
template <typename T1, typename T2>
ostream& operator<<(ostream& os, const map<T1, T2>& v) {
  os << '{';
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) {
      os << ", ";
    }
    os << it->first << ':' << it->second;
  }
  os << '}';
  return os;
}
ll divup(ll nume, ll deno) {
  assert(nume >= 0);
  assert(deno > 0);
  return (nume + deno - 1) / deno;
}
void Yes(void) { cout << "Yes\n"; }
void No(void) { cout << "No\n"; }
void YES(void) { cout << "YES\n"; }
void NO(void) { cout << "NO\n"; }
template <typename T>
bool chmax(T& a, const T& b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T>
bool chmin(T& a, const T& b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T>
void vin(vector<T>& v, ll len) {
  for (ll i = 0; i < (len); i++) {
    cin >> v[i];
  }
}
template <typename Head>
void in_1(Head& h) {
  cin >> h;
}
template <typename Head, typename... Tail>
void in_1(Head& h, Tail&... t) {
  cin >> h;
  in_1(t...);
}
template <typename Head>
void print_1(Head&& h) {
  cout << h << '\n';
}
template <typename Head, typename... Tail>
void print_1(Head&& h, Tail&&... t) {
  cout << h << ' ';
  print_1(t...);
}
void solve() {
  ll N, M;
  in_1(N, M);
  vll num(N, -1);
  for (ll i = 0; i < (M); i++) {
    ll s, c;
    in_1(s, c);
    s--;
    if (num[s] != -1 && num[s] != c) {
      print_1(-1);
      return;
    }
    num[s] = c;
  }
  if (N >= 2 && num[0] == 0) {
    print_1(-1);
    return;
  }
  for (ll i = 0; i < (N); i++) {
    if (num[i] == -1) {
      if (i == 0) {
        num[i] = 1;
      } else {
        num[i] = 0;
      }
    }
  }
  for (ll i = 0; i < (N); i++) {
    printf("%lld", num[i]);
  }
  printf("\n");
}
int main() {
  cout << fixed << setprecision(16);
  cerr << fixed << setprecision(16);
  solve();
}
