#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 = v.size();
  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...);
}
const ll mod = 1000000007LL;
struct mint {
  ll x;
  mint(ll x = 0) : x((x % mod + mod) % mod) {}
  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 {
    mint res(*this);
    return res += a;
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res -= a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res *= a;
  }
  mint pow(ll 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 {
    mint res(*this);
    return res /= a;
  }
  friend ostream& operator<<(ostream& os, const mint& v) {
    os << v.x;
    return os;
  }
};
struct mintcomb {
  vector<mint> fact, ifact;
  mintcomb(int n) : fact(n + 1), ifact(n + 1) {
    assert(n < mod);
    fact[0] = 1;
    for (int i = 1; i <= n; ++i) {
      fact[i] = fact[i - 1] * i;
    }
    ifact[n] = fact[n].inv();
    for (int i = n; i >= 1; --i) {
      ifact[i - 1] = ifact[i] * i;
    }
  }
  mint permutation(int n, int k) {
    if (k < 0 || k > n) return 0;
    return fact[n] * ifact[n - k];
  }
  mint combination(int n, int k) {
    if (k < 0 || k > n) return 0;
    return fact[n] * ifact[k] * ifact[n - k];
  }
};
void solve() {
  ll N, M;
  in_1(N, M);
  vll a(N, -1);
  for (ll i = 0; i < (M); i++) {
    ll s, c;
    in_1(s, c);
    s--;
    if (s == 0 && c == 0 && N > 1) {
      print_1(-1);
      return;
    }
    if (a[s] == -1) {
      a[s] = c;
    } else if (a[s] == c) {
    } else {
      print_1(-1);
      return;
    }
  }
  if (a[0] == -1) {
    a[0] = 1;
  }
  for (ll i = (1); i < (N); i++) {
    if (a[i] == -1) {
      a[i] = 0;
    }
  }
  for (ll i = 0; i < (N); i++) {
    cout << a[i];
  }
  cout << endl;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(16);
  cerr << fixed << setprecision(16);
  solve();
}
