Problem p03050 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bits/stdc++.h>
#include <cmath>
#include <functional>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pullull;
typedef pair<ll, int> plli;
typedef pair<int, pii> pipii;
typedef vector<vector<int>> mati;
typedef vector<vector<double>> matd;
typedef vector<ll> vll;
typedef vector<vector<ll>> vvll;
typedef vector<vector<vector<ll>>> vvvll;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;
typedef vector<vector<vector<bool>>> vvvb;

#define FOR(i, x, y) for (ll i = (ll)x; i < (ll)y; ++i)
#define REP(i, y) FOR(i, 0, y)
#define RFOR(i, x, y) for (ll i = (ll)x; i >= (ll)y; --i)
#define RREP(i, x) RFOR(i, x, 0)

template <typename T> void vec_print(vector<T> VEC) {
  REP(i, VEC.size()) { cout << VEC[i] << " "; }
  cout << "\n";
};

template <typename T>
void mat_print(vector<vector<T>> MAT){
    REP(i, MAT.size()){REP(j, MAT[i].size()){cout << MAT[i][j] << " ";
}
cout << "\n";
}
}
;

template <typename CLASS1, typename CLASS2> class HOGE {
public:
  CLASS1 key;
  CLASS2 value;
  HOGE(void) { return; };
  HOGE(CLASS1 key, CLASS2 value) {
    this->key = key;
    this->value = value;
  };
  ~HOGE(void) { return; };

  void print(void) {
    cout << "key : " << key << ", value : " << value << "\n";
    return;
  };

  bool operator==(const HOGE &obj) { return (this->value == obj.value); };
  bool operator<(const HOGE &obj) { return (this->value < obj.value); };
  bool operator>(const HOGE &obj) { return (this->value > obj.value); };
};

constexpr int INF = (1 << 30);
constexpr ll INFLL = 1LL << 62;
constexpr long double EPS = 1e-12;
constexpr ll MOD = (ll)((1E+9) + 7);

int main() {
  cin.tie(0); // cut the cin and cout (default, std::flush is performed after
              // std::cin)
  ios::sync_with_stdio(
      false); // cut the iostream and stdio (DON'T endl; BUT "\n";)

  ll N;
  cin >> N;

  unordered_set<ll> st;

  ll N_sqrt = (ll)sqrt(N);

  for (ll N_m = 1; N_m <= N_sqrt; ++N_m) {
    ll m = (N - N_m) / N_m;
    if (N / m == N % m)
      st.emplace(m);
  }

  for (ll m = 1; m <= (N / N_sqrt) + 1; ++m) {
    if (N / m == N % m && st.find(m) == st.end())
      st.emplace(m);
  }

  ll ans = 0;
  for (auto itr : st) {
    ans += itr;
  }

  cout << ans << "\n";

  return 0;
}

Fixed submission:
#include <algorithm>
#include <bits/stdc++.h>
#include <cmath>
#include <functional>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pullull;
typedef pair<ll, int> plli;
typedef pair<int, pii> pipii;
typedef vector<vector<int>> mati;
typedef vector<vector<double>> matd;
typedef vector<ll> vll;
typedef vector<vector<ll>> vvll;
typedef vector<vector<vector<ll>>> vvvll;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;
typedef vector<vector<vector<bool>>> vvvb;

#define FOR(i, x, y) for (ll i = (ll)x; i < (ll)y; ++i)
#define REP(i, y) FOR(i, 0, y)
#define RFOR(i, x, y) for (ll i = (ll)x; i >= (ll)y; --i)
#define RREP(i, x) RFOR(i, x, 0)

template <typename T> void vec_print(vector<T> VEC) {
  REP(i, VEC.size()) { cout << VEC[i] << " "; }
  cout << "\n";
};

template <typename T>
void mat_print(vector<vector<T>> MAT){
    REP(i, MAT.size()){REP(j, MAT[i].size()){cout << MAT[i][j] << " ";
}
cout << "\n";
}
}
;

template <typename CLASS1, typename CLASS2> class HOGE {
public:
  CLASS1 key;
  CLASS2 value;
  HOGE(void) { return; };
  HOGE(CLASS1 key, CLASS2 value) {
    this->key = key;
    this->value = value;
  };
  ~HOGE(void) { return; };

  void print(void) {
    cout << "key : " << key << ", value : " << value << "\n";
    return;
  };

  bool operator==(const HOGE &obj) { return (this->value == obj.value); };
  bool operator<(const HOGE &obj) { return (this->value < obj.value); };
  bool operator>(const HOGE &obj) { return (this->value > obj.value); };
};

constexpr int INF = (1 << 30);
constexpr ll INFLL = 1LL << 62;
constexpr long double EPS = 1e-12;
constexpr ll MOD = (ll)((1E+9) + 7);

int main() {
  cin.tie(0); // cut the cin and cout (default, std::flush is performed after
              // std::cin)
  ios::sync_with_stdio(
      false); // cut the iostream and stdio (DON'T endl; BUT "\n";)

  ll N;
  cin >> N;

  unordered_set<ll> st;

  ll N_sqrt = (ll)sqrt(N);

  if (N == 1) {
    cout << "0"
         << "\n";
    return 0;
  }

  for (ll N_m = 1; N_m <= N_sqrt; ++N_m) {
    ll m = (N - N_m) / N_m;
    if (N / m == N % m)
      st.emplace(m);
  }

  for (ll m = 1; m <= (N / N_sqrt) + 1; ++m) {
    if (N / m == N % m && st.find(m) == st.end())
      st.emplace(m);
  }

  ll ans = 0;
  for (auto itr : st) {
    ans += itr;
  }

  cout << ans << "\n";

  return 0;
}