#include <bits/stdc++.h>
using namespace std;
const long long maxx = 1e9 + 7;
bool compare(const pair<long long, long long> &a,
             const pair<long long, long long> &b) {
  return a.first < b.first || (a.first == b.first && a.second < b.second);
}
long long inline power(long long a, long long b, long long p) {
  a %= p;
  long long ans = 1;
  while (b > 0) {
    if (b & 1) ans = (ans * a) % p;
    a = (a * a) % p;
    b >>= 1;
  }
  return ans;
}
long long inv(long long n, long long p) { return power(n, p - 2, p); }
inline vector<long long> allinv(long long n, long long p) {
  vector<long long> arr(n);
  arr[1] = 1;
  for (long long i = (2); i < (n); i += 1) {
    arr[i] = (p - (p / i) * arr[p % i] % p) % p;
  }
  return arr;
}
vector<long long> inline allncr(long long n, long long p) {
  vector<long long> nci(n + 1);
  nci[0] = 1;
  nci[n] = 1;
  vector<long long> v = allinv(n, p);
  for (long long i = (1); i < (n); i += 1) {
    nci[i] = (nci[i - 1] * (n - i - 1)) % p;
  }
  return nci;
}
long long max3(long long a, long long b, long long c) {
  return max(max(a, b), c);
}
bool inline isPrime(long long n) {
  if (n <= 1) return false;
  if (n <= 3) return true;
  if (n % 2 == 0 || n % 3 == 0) return false;
  for (long long i = 5; i * i <= n; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0) return false;
  return true;
}
void prt(int i) { i ? cout << "YES\n" : cout << "NO\n"; }
template <class T>
void printv(T &v) {
  long long n = v.size();
  for (long long i = 0; i < n; i++) cout << v[i] << " ";
  cout << "\n";
}
bool check(long long a, long long b, long long c) {
  if (a == -1 && b == -1 && c == -1) return true;
  return false;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long test = 1;
  while (test--) {
    long long n, m, a, b;
    cin >> n >> m;
    vector<long long> v(3, -1);
    bool poss = true;
    for (long long i = 0; i < m; i++) {
      cin >> a >> b;
      if (v[a - 1] == -1) {
        if (a - 1 == 0 && b == 0 && n > 1) {
          poss = false;
        }
        v[a - 1] = b;
      } else {
        if (v[a - 1] != b) {
          poss = false;
        }
      }
    }
    if (poss) {
      if (v[0] == -1) v[0] = 1;
      if (n > 1 && v[1] == -1) v[1] = 0;
      if (n > 2 && v[2] == -1) v[2] = 0;
      long long ans = 0;
      long long x = 1;
      for (long long i = 0; i < n; i++) {
        ans += v[n - i - 1] * x;
        x *= 10;
      }
      cout << ans << "\n";
    } else
      cout << -1 << "\n";
  }
}
