#include <bits/stdc++.h>
const int N = 3 * 1e5 + 5;
const long long MOD = 998244353;
const long long inf = 1e18;
using namespace std;
long long int MAXN = 100001;
long long int spf[100001];
long long int modpow(long long int x, long long int n) {
  long long int res = 1;
  while (n > 0) {
    if (n & 1) res = res * x % MOD;
    x = x * x % MOD;
    n >>= 1;
  }
  return res;
}
long long int modFact(long long int n, long long int p) {
  if (n >= p) return 0;
  long long int result = 1;
  for (long long int i = 1; i <= n; i++) result = (result * i) % p;
  return result;
}
bool isPrime(int x) {
  if (x % 2 == 0) return 0;
  for (int i = 3; i <= sqrt(x); i += 2) {
    if (x % i == 0) return 0;
  }
  return 1;
}
bool compare(const pair<int, int>& a, const pair<int, int>& b) {
  return a.first < b.first;
}
void solve() {
  int n, m;
  cin >> n >> m;
  int s[m], c[m];
  for (int i = 0; i < m; i++) {
    cin >> s[i] >> c[i];
  }
  if (n == 1) {
    for (int i = 0; i <= 9; i++) {
      int arry[1];
      arry[0] = i;
      bool ok = true;
      for (int j = 0; j < m; j++) {
        ok &= (arry[s[j] - 1] == c[j]);
      }
      if (ok) {
        cout << i;
        return;
      }
    }
  } else if (n == 2) {
    for (int i = 10; i <= 99; i++) {
      int arry[2];
      arry[0] = i % 10;
      arry[1] = (i - i % 10) / 10;
      bool ok = true;
      int tarry[2];
      tarry[0] = arry[1];
      tarry[1] = arry[0];
      for (int j = 0; j < m; j++) {
        ok &= (tarry[s[j] - 1] == c[j]);
      }
      if (ok) {
        cout << i;
        return;
      }
    }
  } else {
    for (int i = 100; i <= 999; i++) {
      int arry[3];
      arry[0] = i % 10;
      arry[1] = ((i - i % 10) / 10) % 10;
      arry[2] = ((i - i % 10) / 10 - ((i - i % 10) / 10) % 10) / 10;
      bool ok = true;
      int tarry[3];
      tarry[0] = arry[2];
      tarry[1] = arry[1];
      tarry[2] = arry[0];
      for (int j = 0; j < m; j++) {
        ok &= (tarry[s[j] - 1] == c[j]);
      }
      if (ok) {
        cout << i;
        return;
      }
    }
  }
  cout << -1;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  int t = 1;
  while (t--) {
    solve();
  }
  cerr << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC
       << "ms\n";
}
