#include <bits/stdc++.h>
using namespace std;
const int MOD = 998244353;
const int MAX = 510000;
const int INF = 1e9;
const double pi = acos(-1);
long long fac[MAX], finv[MAX], inv[MAX];
void COMinit() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < MAX; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}
long long COM(int n, int k) {
  if (n < k) return 0;
  if (n < 0 || k < 0) return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}
int main() {
  COMinit();
  int n, m;
  cin >> n >> m;
  vector<int> s(m);
  vector<int> c(m);
  for (long long i = 0; i < (m); i++) cin >> s[i] >> c[i];
  if (m == 0) {
    if (n != 1)
      cout << pow(10, n - 1) << endl;
    else
      cout << 0 << endl;
    return 0;
  }
  for (int i = pow(10, n - 1); i < pow(10, n); i++) {
    string t = to_string(i);
    bool ok = true;
    for (long long j = 0; j < (m); j++) {
      if (t[s[j] - 1] - '0' != c[j]) {
        ok = false;
        break;
      }
    }
    if (ok) {
      cout << i << endl;
      return 0;
    }
  }
  cout << -1 << endl;
  return 0;
}
