#include <bits/stdc++.h>
using namespace std;
int dx[4] = {0, 0, 1, -1};
int dy[4] = {1, -1, 0, 0};
const int INF = 1 << 29;
const long long MOD = 1000000007;
const int MAX = 200000;
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 modinv(long long a, long long m) {
  long long b = m, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0) u += m;
  return u;
}
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 gcd(int x, int y) { return (x % y) ? gcd(y, x % y) : y; }
int lcm(int x, int y) { return x / gcd(x, y) * y; }
long long com[200005];
void combination(long long n, long long k) {
  com[0] = 1;
  for (int i = 1; i <= k; i++) {
    com[i] = (com[i - 1] * (n - i + 1) % MOD) * modinv(i, MOD) % MOD;
  }
}
int main() {
  int N, M;
  cin >> N >> M;
  vector<int> s(M);
  vector<int> c(M);
  for (int i = 0; i < M; i++) {
    cin >> s[i] >> c[i];
  }
  int loop = 1;
  for (int i = 0; i < N; i++) {
    loop *= 10;
  }
  bool ff = false;
  for (int i = loop / 10; i < loop; i++) {
    cerr << i << endl;
    int x = i / 100;
    int y = (i % 100) / 10;
    int z = i % 10;
    bool f = true;
    for (int j = 0; j < M; j++) {
      if (s[j] == 1) {
        if (x != c[j]) f = false;
      } else if (s[j] == 2) {
        if (y != c[j]) f = false;
      } else {
        if (z != c[j]) f = false;
      }
      if (!f) break;
    }
    if (f) {
      cout << i << endl;
      ff = true;
      break;
    }
  }
  if (!ff) cout << -1 << endl;
  return 0;
}
