Problem p02819 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) (int)((x).size())
#define debug(x) cout << #x << ":" << x << ' ';
#define debugg(x) cout << #x << ":" << x << ' ' << "\n";
#define endl "\n"
#define L(X) ((X) << 1)
#define R(X) (((X) << 1) | 1)
#define M(X, Y) (((X) + (Y)) >> 1)

using namespace std;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

const int MAXN = 2e5 + 5;
const int MOD = 1e9 + 7;
const int INF = 0x3f3f3f3f;
const long long int LLINF = 0x3f3f3f3f3f3f3f3f;
const double EPS = 1e-9;
const double PI = acos(-1);

template <typename T> T max_self(T &a, T b) {
  if (a < b)
    a = b;
  return a;
}
template <typename T> T min_self(T &a, T b) {
  if (a > b)
    a = b;
  return a;
}
template <typename T> T add(T x, T y) { return ((x % MOD) + (y % MOD)) % MOD; }
template <typename T> T mul(T x, T y) {
  return ((x % MOD) * (long long)(y % MOD)) % MOD;
}
template <typename T> T sub(T x, T y) { return add(x, -y + MOD); }
template <typename T> T gcd(T a, T b) { return b ? gcd(b, a % b) : a; }
template <typename T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
template <typename T> vector<T> read(vector<T> &v, int n) {
  v.resize(n);
  for (auto &x : v)
    cin >> x;
}
template <typename T> void trav(vector<T> &v) {
  for (int i = 0; i < (int)v.size(); ++i) {
    cout << v[i];
    if (i != (int)v.size() - 1)
      cout << ' ';
  }
}
int lg2(long long x) { return 64 - __builtin_clzll(x) - 1; }
int lg2(int x) { return 32 - __builtin_clzll(x) - 1; }

struct pair_hash {
  template <class T1, class T2> size_t operator()(const pair<T1, T2> &p) const {
    auto h1 = hash<T1>{}(p.first);
    auto h2 = hash<T2>{}(p.second);
    return h1 ^ h2;
  }
};

int x;
bool prime[MAXN];

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);

  set<int> pr;

  memset(prime, true, sizeof prime);

  prime[2] = true;

  for (int i = 2; i <= MAXN; ++i) {
    if (prime[i]) {
      pr.insert(i);
      for (int j = 2 * i; j <= MAXN; j += i) {
        prime[j] = false;
      }
    }
  }

  int x;
  cin >> x;

  cout << *pr.lower_bound(x) << endl;

  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) (int)((x).size())
#define debug(x) cout << #x << ":" << x << ' ';
#define debugg(x) cout << #x << ":" << x << ' ' << "\n";
#define endl "\n"
#define L(X) ((X) << 1)
#define R(X) (((X) << 1) | 1)
#define M(X, Y) (((X) + (Y)) >> 1)

using namespace std;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

const int MAXN = 2e5 + 5;
const int MOD = 1e9 + 7;
const int INF = 0x3f3f3f3f;
const long long int LLINF = 0x3f3f3f3f3f3f3f3f;
const double EPS = 1e-9;
const double PI = acos(-1);

template <typename T> T max_self(T &a, T b) {
  if (a < b)
    a = b;
  return a;
}
template <typename T> T min_self(T &a, T b) {
  if (a > b)
    a = b;
  return a;
}
template <typename T> T add(T x, T y) { return ((x % MOD) + (y % MOD)) % MOD; }
template <typename T> T mul(T x, T y) {
  return ((x % MOD) * (long long)(y % MOD)) % MOD;
}
template <typename T> T sub(T x, T y) { return add(x, -y + MOD); }
template <typename T> T gcd(T a, T b) { return b ? gcd(b, a % b) : a; }
template <typename T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
template <typename T> vector<T> read(vector<T> &v, int n) {
  v.resize(n);
  for (auto &x : v)
    cin >> x;
}
template <typename T> void trav(vector<T> &v) {
  for (int i = 0; i < (int)v.size(); ++i) {
    cout << v[i];
    if (i != (int)v.size() - 1)
      cout << ' ';
  }
}
int lg2(long long x) { return 64 - __builtin_clzll(x) - 1; }
int lg2(int x) { return 32 - __builtin_clzll(x) - 1; }

struct pair_hash {
  template <class T1, class T2> size_t operator()(const pair<T1, T2> &p) const {
    auto h1 = hash<T1>{}(p.first);
    auto h2 = hash<T2>{}(p.second);
    return h1 ^ h2;
  }
};

int x;
bool prime[MAXN + 1];

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);

  set<int> pr;

  memset(prime, true, sizeof prime);

  prime[2] = true;

  for (int i = 2; i <= MAXN; ++i) {
    if (prime[i]) {
      pr.insert(i);
      for (int j = 2 * i; j <= MAXN; j += i) {
        prime[j] = false;
      }
    }
  }

  int x;
  cin >> x;

  cout << *pr.lower_bound(x) << endl;

  return 0;
}