#include <bits/stdc++.h>
using namespace std;
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
const long long P = 1000000007;
long long factorial(long long n) {
  long long ans = 1;
  for (int i = n; i >= 1; i--) {
    ans *= i;
    ans %= P;
  }
  return ans;
}
using Graph = vector<vector<int>>;
long long kzyou(long long a, long long k) {
  long long zyou = 1;
  for (long long i = 1; i <= k; i++) {
    zyou *= a;
  }
  return zyou;
}
int main() {
  int N, M;
  cin >> N >> M;
  vector<pair<int, int>> p(M);
  for (int i = 0; i < (int)(M); i++) {
    cin >> p[i].first >> p[i].second;
  }
  long long ketaN = kzyou(10, N - 1);
  sort(p.begin(), p.end());
  if (N == 1 && M == 0)
    cout << 0 << endl;
  else {
    bool flag = true;
    for (int i = 0; i < M - 1; i++) {
      if (p[i].first == p[i + 1].first) {
        if (p[i].second != p[i + 1].second) flag = false;
      }
    }
    if (!flag)
      cout << -1 << endl;
    else if (flag) {
      set<pair<int, int>> S;
      for (int i = 0; i < (int)(M); i++) {
        S.insert(p[i]);
      }
      int ans = 0;
      bool flag1 = false;
      for (auto value : S) {
        int k = value.first;
        int C = value.second;
        if (k == 1) flag1 = true;
        if (k == 1 && C == 0) {
          flag = false;
          break;
        }
        ans += kzyou(10, N - k) * C;
      }
      if (flag == false)
        cout << -1 << endl;
      else if (!flag1) {
        ans += kzyou(10, N - 1);
        cout << ans << endl;
      } else
        cout << ans << endl;
    }
  }
}
