#include <bits/stdc++.h>
using namespace std;
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
const int INF = 1001001001;
vector<pair<int64_t, int64_t>> func(int64_t x) {
  vector<pair<int64_t, int64_t>> p;
  for (int64_t i = 2; i * i <= x; i++) {
    int cnt = 0;
    if (x % i == 0) {
      while (x % i == 0) {
        cnt++;
        x /= i;
      }
      p.push_back(make_pair(i, cnt));
    }
  }
  if (x != 1) {
    p.push_back(make_pair(x, 1));
  }
  return p;
}
int main() {
  int N, M;
  cin >> N >> M;
  int s[10];
  int c[10];
  for (int i = 0; i < M; i++) {
    cin >> s[i] >> c[i];
  }
  for (int j = 0; j <= 999; j++) {
    vector<int> d(1, j % 10);
    int x = j;
    while (x / 10 > 0) {
      d.push_back(x % 10);
      x /= 10;
    }
    bool ok = true;
    reverse(d.begin(), d.end());
    if (d.size() != N) {
      continue;
    }
    for (int i = 0; i < M; i++) {
      if (d[s[i] - 1] != c[i]) {
        ok = false;
      }
    }
    if (ok) {
      cout << j << endl;
      return 0;
    }
  }
  cout << -1 << endl;
  return 0;
}
