Problem p04048 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <string>
#include <vector>

#define REP(i, n) for (int i = 0; i < n; i++)
#define REPR(i, n) for (int i = n; i >= 0; i--)
#define FOR(i, m, n) for (int i = m; i < n; i++)
#define FORR(i, m, n) for (int i = m; i >= n; i--)
#define SORT(v, n) sort(v, v + n);
#define VSORT(v) sort(v.begin(), v.end());
#define REVERSE(v, n) reverse(v, v + n);
#define VREVERSE(v) reverse(v.begin(), v.end());
#define ll long long
#define pb(a) push_back(a)
#define INF 9999999999
#define m0(x) memset(x, 0, sizeof(x))
#define fill(x, y) memset(x, y, sizeof(x))
#define print(x) cout << x << endl;
#define pe(x) cout << x << " ";
#define lb(v, n) lower_bound(v.begin(), v.end(), n);
// #define int long long

using namespace std;

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

int dy[4] = {0, 0, 1, -1};
int dx[4] = {1, -1, 0, 0};
int dxx[9] = {0, 0, 0, 1, 1, 1, -1, -1, -1};
int dyy[9] = {0, 1, -1, 0, 1, -1, 0, 1, -1};

ll gcd(ll x, ll y) {
  ll m = max(x, y), n = min(x, y);
  if (m % n == 0)
    return n;
  else
    return gcd(m % n, n);
}
ll lcm(ll x, ll y) { return x / gcd(x, y) * y; }

long long power_mod(long long x, long long n, long long m) {
  if (n == 0)
    return 1;
  if (n % 2 == 0)
    return power_mod(x * x % m, n / 2, m);
  else
    return x * power_mod(x, n - 1, m) % m;
}

long long power(long long a, long long n) { // aのn乗を計算します。
  long long x = 1;
  while (n > 0) { // 全てのbitが捨てられるまで。
    if (n & 1) {  // 1番右のbitが1のとき。
      x = x * a;
    }
    a = a * a;
    n >>= 1; // bit全体を右に1つシフトして一番右を捨てる。
  }
  return x;
}

long long nCr(long long n, long long r) {
  if (r > n / 2)
    r = n - r; // because C(n, r) == C(n, n - r)
  long long ans = 1;
  long long i;

  for (i = 1; i <= r; i++) {
    ans *= n - r + i;
    ans /= i;
  }

  return ans;
}

const int MAX = 510000;
const int MOD = 1000000007;

long long fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
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;
  }
}

// 二項係数計算
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;
}

bool arr[100000100];
vector<ll> sosuu;
void Eratosthenes() {
  ll N = 10000010;
  int c = 0;
  for (int i = 0; i < N; i++) {
    arr[i] = 1;
  }
  for (ll i = 2; i < sqrt(N); i++) {
    if (arr[i]) {
      for (ll j = 0; i * (j + 2) < N; j++) {
        arr[i * (j + 2)] = 0;
      }
    }
  }

  for (ll i = 2; i < N; i++) {
    if (arr[i]) {
      sosuu.pb(i);
      // cout << sosuu[c] << " ";
      c++;
    }
  }
  // cout << endl;
  // cout << c << endl;
}

ll stoL(string s) {
  ll n = s.length();
  ll ans = 0;
  for (int i = 0; i < n; i++) {
    ans += power(10, n - i - 1) * (ll)(s[i] - '0');
  }
  return ans;
}

ll func(ll a, ll b) {
  if (a > b) {
    ll tmp = a;
    a = b;
    b = tmp;
  }
  if (a == b) {
    return a;
  } else if (b > 2 * a) {
    ll c = b / a;
    return 2 * a * c + func(b - a * c, a);
  } else
    return 2 * a + func(b - a, a);
}
int main() {
  ll N, X;
  cin >> N >> X;
  ll ans = N + func(X, N - X);
  print(ans);
}


Fixed submission:
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <string>
#include <vector>

#define REP(i, n) for (int i = 0; i < n; i++)
#define REPR(i, n) for (int i = n; i >= 0; i--)
#define FOR(i, m, n) for (int i = m; i < n; i++)
#define FORR(i, m, n) for (int i = m; i >= n; i--)
#define SORT(v, n) sort(v, v + n);
#define VSORT(v) sort(v.begin(), v.end());
#define REVERSE(v, n) reverse(v, v + n);
#define VREVERSE(v) reverse(v.begin(), v.end());
#define ll long long
#define pb(a) push_back(a)
#define INF 9999999999
#define m0(x) memset(x, 0, sizeof(x))
#define fill(x, y) memset(x, y, sizeof(x))
#define print(x) cout << x << endl;
#define pe(x) cout << x << " ";
#define lb(v, n) lower_bound(v.begin(), v.end(), n);
// #define int long long

using namespace std;

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

int dy[4] = {0, 0, 1, -1};
int dx[4] = {1, -1, 0, 0};
int dxx[9] = {0, 0, 0, 1, 1, 1, -1, -1, -1};
int dyy[9] = {0, 1, -1, 0, 1, -1, 0, 1, -1};

ll gcd(ll x, ll y) {
  ll m = max(x, y), n = min(x, y);
  if (m % n == 0)
    return n;
  else
    return gcd(m % n, n);
}
ll lcm(ll x, ll y) { return x / gcd(x, y) * y; }

long long power_mod(long long x, long long n, long long m) {
  if (n == 0)
    return 1;
  if (n % 2 == 0)
    return power_mod(x * x % m, n / 2, m);
  else
    return x * power_mod(x, n - 1, m) % m;
}

long long power(long long a, long long n) { // aのn乗を計算します。
  long long x = 1;
  while (n > 0) { // 全てのbitが捨てられるまで。
    if (n & 1) {  // 1番右のbitが1のとき。
      x = x * a;
    }
    a = a * a;
    n >>= 1; // bit全体を右に1つシフトして一番右を捨てる。
  }
  return x;
}

long long nCr(long long n, long long r) {
  if (r > n / 2)
    r = n - r; // because C(n, r) == C(n, n - r)
  long long ans = 1;
  long long i;

  for (i = 1; i <= r; i++) {
    ans *= n - r + i;
    ans /= i;
  }

  return ans;
}

const int MAX = 510000;
const int MOD = 1000000007;

long long fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
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;
  }
}

// 二項係数計算
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;
}

bool arr[100000100];
vector<ll> sosuu;
void Eratosthenes() {
  ll N = 10000010;
  int c = 0;
  for (int i = 0; i < N; i++) {
    arr[i] = 1;
  }
  for (ll i = 2; i < sqrt(N); i++) {
    if (arr[i]) {
      for (ll j = 0; i * (j + 2) < N; j++) {
        arr[i * (j + 2)] = 0;
      }
    }
  }

  for (ll i = 2; i < N; i++) {
    if (arr[i]) {
      sosuu.pb(i);
      // cout << sosuu[c] << " ";
      c++;
    }
  }
  // cout << endl;
  // cout << c << endl;
}

ll stoL(string s) {
  ll n = s.length();
  ll ans = 0;
  for (int i = 0; i < n; i++) {
    ans += power(10, n - i - 1) * (ll)(s[i] - '0');
  }
  return ans;
}

ll func(ll a, ll b) {
  if (a > b) {
    ll tmp = a;
    a = b;
    b = tmp;
  }
  if (a == b) {
    return a;
  } else {
    if (b % a == 0) {
      ll c = b / a;
      return 2 * a * c - a;
    } else {
      ll c = b / a;
      return 2 * a * c + func(b - a * c, a);
    }
  }
}
int main() {
  ll N, X;
  cin >> N >> X;
  ll ans = N + func(X, N - X);
  print(ans);
}