#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vs = vector<string>;
using vvs = vector<vs>;
using vc = vector<char>;
using vvc = vector<vc>;
using vb = vector<bool>;
using vvb = vector<vb>;
bool is_int_lround(double x) { return std::lround(x) == x; }
ll keta(ll x) {
  ll n = 0;
  while (x > 0) {
    x /= 10;
    n++;
  }
  return n;
}
ll conbi(int n, int m) {
  cin >> n >> m;
  vector<ll> a(100);
  a[0] = 1;
  for (int i = 0; i < 14; i++) {
    a[i + 1] = a[i] * (i + 1);
  }
  return a[n] / (a[m] * a[n - m]);
}
long long modpow(long long a, long long n, long long mod) {
  long long res = 1;
  while (n > 0) {
    if (n & 1) res = res * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return res;
}
ll kaijo(ll x) {
  ll z = 1;
  while (x > 0) {
    z *= x;
    z %= 1000000007;
    x--;
  }
  return z;
}
ll yakusu_num(ll n) {
  vl yakusu(n + 1, 1);
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      n /= i;
      yakusu[i]++;
    }
  }
  if (n != 1) yakusu[n]++;
  ll num = 1;
  for (ll i = 0; i <= n; i++) {
    num *= yakusu[i];
  }
  return num;
}
int main() {
  int N, M;
  cin >> N >> M;
  vi s(M);
  vc c(M);
  ;
  for (int i = 0; i < M; i++) cin >> s[i] >> c[i];
  string ans = "-1";
  for (int i = 1; i < 1000; i++) {
    string st = to_string(i);
    if (st.size() != N) continue;
    bool ok = true;
    ;
    for (int j = 0; j < M; j++) {
      if (st[s[j] - 1] != c[j]) ok = false;
    }
    if (ok) {
      ans = st;
      break;
    }
  }
  cout << ans << endl;
}
