Problem p02994 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
#define IO()                                                                   \
  assert(freopen("in.in", "rt", stdin)),                                       \
      assert(freopen("out.out", "wt", stdout))
#define FastIO() ios::sync_with_stdio(false);
#define debug(x) cout << __LINE__ << ": " << #x << " = " << (x) << endl

inline int readChar();
template <class T = int> inline T readInt();
template <class T> inline void writeInt(T x, char end = 0);
inline void writeChar(int x);
inline void writeWord(const char *s);

/** Read */

static const int buf_size = 4096;

inline int getChar() {
  static char buf[buf_size];
  static int len = 0, pos = 0;
  if (pos == len)
    pos = 0, len = fread(buf, 1, buf_size, stdin);
  if (pos == len)
    return -1;
  return buf[pos++];
}

inline int readChar() {
  int c = getChar();
  while (c <= 32)
    c = getChar();
  return c;
}

template <class T> inline T readInt() {
  int s = 1, c = readChar();
  T x = 0;
  if (c == '-')
    s = -1, c = getChar();
  while ('0' <= c && c <= '9')
    x = x * 10 + c - '0', c = getChar();
  return s == 1 ? x : -x;
}

/** Write */

static int write_pos = 0;
static char write_buf[buf_size];

inline void writeChar(int x) {
  if (write_pos == buf_size)
    fwrite(write_buf, 1, buf_size, stdout), write_pos = 0;
  write_buf[write_pos++] = x;
}

template <class T> inline void writeInt(T x, char end) {
  if (x < 0)
    writeChar('-'), x = -x;

  char s[24];
  int n = 0;
  while (x || !n)
    s[n++] = '0' + x % 10, x /= 10;
  while (n--)
    writeChar(s[n]);
  if (end)
    writeChar(end);
}

inline void writeWord(const char *s) {
  while (*s)
    writeChar(*s++);
}

struct Flusher {
  ~Flusher() {
    if (write_pos)
      fwrite(write_buf, 1, write_pos, stdout), write_pos = 0;
  }
} flusher;

typedef long long ll;
const ll MOD = 1e9 + 7;
const int N = 1e7 + 9, M = 1e5 + 9, OO = 0x3f3f3f3f;
const double EPS = 1e-10;

int main() {
#ifndef ONLINE_JUDGE
  IO();
#endif
  int n = readInt(), l = readInt();
  int mn = OO;
  ll sum = 0;
  for (int i = 0; i < n; ++i) {
    int x = l + i;
    sum += x;
    mn = (abs(mn) > abs(x)) ? x : mn;
  }
  writeInt(sum - mn);
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define IO()                                                                   \
  assert(freopen("in.in", "rt", stdin)),                                       \
      assert(freopen("out.out", "wt", stdout))
#define FastIO() ios::sync_with_stdio(false);
#define debug(x) cout << __LINE__ << ": " << #x << " = " << (x) << endl

inline int readChar();
template <class T = int> inline T readInt();
template <class T> inline void writeInt(T x, char end = 0);
inline void writeChar(int x);
inline void writeWord(const char *s);

/** Read */

static const int buf_size = 4096;

inline int getChar() {
  static char buf[buf_size];
  static int len = 0, pos = 0;
  if (pos == len)
    pos = 0, len = fread(buf, 1, buf_size, stdin);
  if (pos == len)
    return -1;
  return buf[pos++];
}

inline int readChar() {
  int c = getChar();
  while (c <= 32)
    c = getChar();
  return c;
}

template <class T> inline T readInt() {
  int s = 1, c = readChar();
  T x = 0;
  if (c == '-')
    s = -1, c = getChar();
  while ('0' <= c && c <= '9')
    x = x * 10 + c - '0', c = getChar();
  return s == 1 ? x : -x;
}

/** Write */

static int write_pos = 0;
static char write_buf[buf_size];

inline void writeChar(int x) {
  if (write_pos == buf_size)
    fwrite(write_buf, 1, buf_size, stdout), write_pos = 0;
  write_buf[write_pos++] = x;
}

template <class T> inline void writeInt(T x, char end) {
  if (x < 0)
    writeChar('-'), x = -x;

  char s[24];
  int n = 0;
  while (x || !n)
    s[n++] = '0' + x % 10, x /= 10;
  while (n--)
    writeChar(s[n]);
  if (end)
    writeChar(end);
}

inline void writeWord(const char *s) {
  while (*s)
    writeChar(*s++);
}

struct Flusher {
  ~Flusher() {
    if (write_pos)
      fwrite(write_buf, 1, write_pos, stdout), write_pos = 0;
  }
} flusher;

typedef long long ll;
const ll MOD = 1e9 + 7;
const int N = 1e7 + 9, M = 1e5 + 9, OO = 0x3f3f3f3f;
const double EPS = 1e-10;

int main() {
#ifdef _LOCAL_DEFINE
  IO();
#endif
  int n = readInt(), l = readInt();
  int mn = OO;
  ll sum = 0;
  for (int i = 0; i < n; ++i) {
    int x = l + i;
    sum += x;
    mn = (abs(mn) > abs(x)) ? x : mn;
  }
  writeInt(sum - mn);
  return 0;
}