#include <bits/stdc++.h>
using namespace std;
long long int mpow(long long int a, long long int b) {
  if (b == 0)
    return 1;
  else if (b % 2 == 0) {
    long long int memo = mpow(a, b / 2);
    return memo * memo % (long long int)(1e9 + 7);
  } else
    return mpow(a, b - 1) * a % (long long int)(1e9 + 7);
}
long long int lpow(long long int a, long long int b) {
  if (b == 0)
    return 1;
  else if (b % 2 == 0) {
    long long int memo = lpow(a, b / 2);
    return memo * memo;
  } else
    return lpow(a, b - 1) * a;
}
long long int gcd(long long int a, long long int b) {
  if (b == 0)
    return a;
  else
    return gcd(b, a % b);
}
vector<long long int> kaijo_memo;
long long int kaijo(long long int n) {
  if (kaijo_memo.size() > n) return kaijo_memo[n];
  if (kaijo_memo.size() == 0) kaijo_memo.push_back(1);
  while (kaijo_memo.size() <= n)
    kaijo_memo.push_back(kaijo_memo[kaijo_memo.size() - 1] * kaijo_memo.size() %
                         (long long int)(1e9 + 7));
  return kaijo_memo[n];
}
vector<long long int> gyaku_kaijo_memo;
long long int gyaku_kaijo(long long int n) {
  if (gyaku_kaijo_memo.size() > n) return gyaku_kaijo_memo[n];
  if (gyaku_kaijo_memo.size() == 0) gyaku_kaijo_memo.push_back(1);
  while (gyaku_kaijo_memo.size() <= n)
    gyaku_kaijo_memo.push_back(
        gyaku_kaijo_memo[gyaku_kaijo_memo.size() - 1] *
        mpow(gyaku_kaijo_memo.size(), (long long int)(1e9 + 7) - 2) %
        (long long int)(1e9 + 7));
  return gyaku_kaijo_memo[n];
}
long long int nCr(long long int n, long long int r) {
  if (n == r) return 1;
  if (n < r || r < 0) return 0;
  long long int ret = 1;
  if (n <= 1e7) {
    ret *= kaijo(n);
    ret %= (long long int)(1e9 + 7);
    ret *= gyaku_kaijo(r);
    ret %= (long long int)(1e9 + 7);
    ret *= gyaku_kaijo(n - r);
    ret %= (long long int)(1e9 + 7);
  } else {
    for (int i = 0; i < (int)(r); i++) {
      ret *= n - i;
      ret %= (long long int)(1e9 + 7);
      ret *= mpow(r - i, (long long int)(1e9 + 7) - 2);
      ret %= (long long int)(1e9 + 7);
    }
  }
  return ret;
}
int main(void) {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout << fixed << setprecision(15);
  long long int n, m;
  cin >> n >> m;
  vector<int> ans(n, -1);
  bool ok = true;
  for (int t = 0; t < (int)(m); t++) {
    int s, c;
    cin >> s >> c;
    if (ans[s - 1] != -1 && ans[s - 1] != c) {
      ok = false;
    }
    ans[s - 1] = c;
  }
  if (ans[0] == 0 && n != 1) {
    ok = false;
  }
  if (!ok) {
    cout << -1 << endl;
    return 0;
  }
  for (int t = 0; t < (int)(n); t++) {
    if (ans[t] == -1) {
      if (t == 0 && n == 0) {
        ans[t] = 0;
      } else if (t == 0 && n != 0) {
        ans[t] = 1;
      } else {
        ans[t] = 0;
      }
    }
  }
  for (int t = 0; t < (int)(n); t++) {
    cout << ans[t];
  }
  cout << endl;
  return 0;
}
