#include <bits/stdc++.h>
using namespace std;
const int MAX = 700000;
const int MOD = 1000000007;
long long fac[MAX], finv[MAX], inv[MAX];
void COMinit() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < MAX; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}
long long COM(int n, int k) {
  if (n < k) return 0;
  if (n < 0 || k < 0) return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}
long long int maxtime(long long int x, long long int y) {
  return (x + y - 1) / y;
}
long long int lcm(long long int number1, long long int number2) {
  long long int m = number1;
  long long int n = number2;
  if (number2 > number1) {
    m = number2;
    n = number1;
  }
  long long int s = -1;
  while (s != 0) {
    s = m % n;
    m = n;
    n = s;
  }
  return m;
}
long long int gcd(long long int number1, long long int number2) {
  long long int m = number1;
  long long int n = number2;
  return m / lcm(m, n) * n;
}
long long int modinv(long long a, long long m) {
  long long int b = m, u = 1, v = 0;
  while (b) {
    long long int t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0) u += m;
  return u;
}
vector<long long int> meguru;
bool isOK(int index, int key) {
  if (meguru[index] >= key)
    return true;
  else
    return false;
}
int binary_search(int key) {
  int left = -1;
  int right = (int)meguru.size();
  while (right - left > 1) {
    int mid = left + (right - left) / 2;
    if (isOK(mid, key))
      right = mid;
    else
      left = mid;
  }
  return right;
}
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;
}
int main() {
  int n, m;
  cin >> n >> m;
  vector<pair<int, int>> s;
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    s.push_back(make_pair(a, b));
  }
  for (int i = 0; i <= 999; i++) {
    int dp[3] = {};
    int number = i;
    int keta = 0;
    if (i == 0) {
      keta = 1;
    } else {
      keta = 0;
    }
    while (number) {
      number = number / 10;
      keta++;
    }
    number = i;
    for (int j = 0; j < 3; j++) {
      dp[j] = number % 10;
      number = number / 10;
    }
    for (int j = 0; j < m; j++) {
      if (dp[3 - s[j].first] != s[j].second) {
        break;
      }
      if (j == m - 1 && keta == n) {
        cout << i;
        return 0;
      }
    }
  }
  cout << -1;
}
