#include <bits/stdc++.h>
using namespace std;
const double pi = acos(-1.0L);
const long long mod = 1e9 + 7;
long long dy[4] = {1, 0, -1, 0};
long long dx[4] = {0, 1, 0, -1};
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class A, class B>
ostream& operator<<(ostream& ost, const pair<A, B>& p) {
  ost << "{" << p.first << ", " << p.second << "} ";
  return ost;
}
template <class T>
ostream& operator<<(ostream& ost, const vector<T>& v) {
  ost << "{";
  for (int i = 0; i < v.size(); i++) {
    if (i) ost << ", ";
    ost << v[i];
  }
  ost << "} ";
  return ost;
}
template <class A, class B>
ostream& operator<<(ostream& ost, const map<A, B>& v) {
  ost << "{";
  for (auto p : v) {
    ost << "{" << p.first << ", " << p.second << "} ";
  }
  ost << "} ";
  return ost;
}
bool out_check(long long a, long long b) { return (0 <= a && a < b); }
double pitagoras(long long a, long long b, long long c, long long d) {
  double dx = a - b, dy = c - d;
  return pow(dx * dx + dy * dy, 0.5);
}
long long modpow(long long a, long long b) {
  long long c = 1;
  while (b > 0) {
    if (b & 1) {
      c = a * c % mod;
    }
    a = a * a % mod;
    b >>= 1;
  }
  return c;
}
void Yes(bool x) { cout << ((x) ? "Yes\n" : "No\n"); }
void YES(bool x) { cout << ((x) ? "YES\n" : "NO\n"); }
void yes(bool x) { cout << ((x) ? "yes\n" : "no\n"); }
void Yay(bool x) { cout << ((x) ? "Yay!\n" : ":(\n"); }
long long n, m, d, e, r, l, k, h, w, Q, ans, ret = LLONG_MAX;
bool flag = false, flag2 = false, flag3 = false;
string s, t, u;
long long x, y;
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> m;
  vector<long long> a(n, 0);
  a[0] = -1;
  for (int i = 0; i < m; ++i) {
    cin >> d >> e;
    d--;
    if (a[d] && a[d] != e) {
      if (d == 0 && a[d] == -1)
        a[d] = e;
      else {
        cout << "-1" << endl;
        return 0;
      }
    } else {
      a[d] = e;
    }
  }
  for (int i = 0; i < n; ++i) s += to_string(a[i]);
  if (s[0] == '0') s = "-1";
  cout << s << endl;
  return 0;
}
