#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-8;
const int MOD = 1000000007;
const int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
const int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1},
          dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T &a, U b) {
  return a < b ? (a = b, true) : false;
}
template <typename T, typename U>
inline bool chmin(T &a, U b) {
  return a > b ? (a = b, true) : false;
}
struct IOSetup {
  IOSetup() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  }
} iosetup;
int main() {
  int n, m;
  cin >> n >> m;
  int mx = 1;
  for (int _ = (0); _ < (n); ++_) mx *= 10;
  vector<int> s(m), c(m);
  for (int i = (0); i < (m); ++i) {
    cin >> s[i] >> c[i];
    --s[i];
    s[i] = n - 1 - s[i];
  }
  for (int ans = (0); ans < (mx); ++ans) {
    string str = to_string(ans);
    reverse((str).begin(), (str).end());
    bool ok = true;
    for (int i = (0); i < (m); ++i)
      ok &= str.length() > s[i] && str[s[i]] - '0' == c[i];
    if (ok) {
      cout << ans << '\n';
      return 0;
    }
  }
  cout << "-1\n";
  return 0;
}
