Problem p03319 (C++)

Buggy submission (status: Runtime Error):
// include
//------------------------------------------
#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
using namespace std;
// conversion
//------------------------------------------
inline int toInt(string s) {
  int v;
  istringstream sin(s);
  sin >> v;
  return v;
}
template <class T> inline string toString(T x) {
  ostringstream sout;
  sout << x;
  return sout.str();
}
// math
//-------------------------------------------
template <class T> inline T sqr(T x) { return x * x; }
// typedef
//------------------------------------------
typedef long long ll;
typedef long long LL;
typedef vector<long long> VLL;
typedef vector<long long> vll;
typedef pair<long long, long long> pll;
typedef pair<long long, long long> PLL;

// container util
//------------------------------------------
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define VECMAX(x) *max_element(ALL(x))
#define VECMIN(x) *min_element(ALL(x))
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i, c)                                                             \
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())
// repetition
//------------------------------------------
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)
#define MULTIPLE(i, n, k) for (int i = (k); i < (n); i += k + 1) // 倍数ループ
// constant
//------------------------------------------
const double EPS = 1e-10;
const double PI = acos(-1.0);
// clear memory
#define CLR(a) memset((a), 0, sizeof(a))
// debug
#define dump(x) cerr << #x << " = " << (x) << endl;
#define debug(x)                                                               \
  cerr << #x << " = " << (x) << " (L" << __LINE__ << ")"                       \
       << " " << __FILE__ << endl;
#define SIZEOF(x) sizeof(x) / sizeof(x[0])

const long long INF = 100000000000000;
const long long NINF = -100000000000000;

//----------------search for specific figure--------------------
//--------------------------------------------------------------

ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
ll nCr(ll n, ll r) {

  if (n == 0) {
    return 0;
  }
  if (r == 0) {
    return 1;
  }
  if (r == 1) {
    return n;
  }
  if (n == r) {
    return 1;
  }

  if (r > n / 2) {
    r = n / 2;
  }

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

// firstが最大値（最小値） , second が index
pair<LL, LL> maxP(vll a, ll size) {
  pair<ll, ll> p;
  vll::iterator iter = max_element(a.begin(), a.end());
  p.first = *iter;
  p.second = distance(a.begin(), iter);
  return p;
}

pair<LL, LL> minP(vll a, ll size) {
  pair<ll, ll> p;
  vll::iterator iter = min_element(a.begin(), a.end());
  p.first = *iter;
  p.second = distance(a.begin(), iter);
  return p;
}

ll sumL(vll a, ll size) {
  ll sum = 0;
  REP(i, size) { sum += a[i]; }
  return sum;
}

// aのなかにtがいくつあるか
ll counT(VLL a, ll t) {

  sort(a.begin(), a.end());
  return upper_bound(a.begin(), a.end(), t) -
         lower_bound(a.begin(), a.end(), t);
}

#define COUNT(a, b) counT((a), (b))
#define MAX(x) maxP(x, x.size())
#define MIN(x) minP(x, x.size())
#define SUM(x) sumL(x, x.size())

//-------------------DIVIDE----------------------
// DIV[i][j] は　i の j分割数 j == 0 && i != 0 なら 0
// 並び順を区別しない

ll DIV[1000 + 1][1000 + 1];
void divide(ll n, ll m) {
  DIV[0][0] = 1;
  FOR(i, 1, n + 1) { DIV[i][0] = 0; }
  REP(i, n + 1) { DIV[i][1] = 1; }
  FOR(i, 1, m + 1) {
    FOR(t, 0, n + 1) {
      if (DIV[t][i] > 0)
        continue;
      if (t >= i) {
        DIV[t][i] = DIV[t - i][i] + DIV[t][i - 1];
      } else {
        DIV[t][i] = DIV[t][i - 1];
      }
    }
  }
}
#define DIVIDE(a, b) (DIV[a][b] - DIV[a][(b)-1])

//-------要素を見つける-----------

ll search(vll &a, ll n) { // a内のnのindexを返す
  std::vector<ll>::iterator iter = std::find(a.begin(), a.end(), n);
  size_t index = distance(a.begin(), iter);
  return index;
}

//------------素数判定-----------------

//------------素数判定-----------------
vector<bool> IS_PRIME_CONTAINER(1000005, true);
// メモリを圧迫する可能性あり

void IsPrime_Contain(ll num) {
  IS_PRIME_CONTAINER[0] = false;
  IS_PRIME_CONTAINER[1] = false;
  FOR(i, 2, sqrt(num) + 1) {
    if (IS_PRIME_CONTAINER[i]) {
      FOR(j, 2, num / i + 1) {
        if (j * i <= num) {
          IS_PRIME_CONTAINER[i * j] = false;
        }
      }
    }
  }
}

inline bool IsPrime(ll num) { return IS_PRIME_CONTAINER[num]; }

//---------ベルマンフォード----------
struct E {
  ll from, to, cost;
};
ll DIST[100005];
// start と 辺の数 m 辺の情報 x を入力
void shortest(LL s, vector<E> &x, ll m) {
  REP(i, 100000) { DIST[i] = INF; }
  DIST[s] = 0;
  while (1) {
    bool t = false;
    REP(i, m) {
      E h = x[i];
      if (DIST[h.from] != INF && DIST[h.to] > DIST[h.from] + h.cost) {
        DIST[h.to] = DIST[h.from] + h.cost;
        t = true;
      }
    }
    if (!t) {
      break;
    }
  }
}

//----UnionFind-----

class UnionFind {
public:
  vll par;
  vll rank; // rankが高いほど上の親である
  UnionFind(LL N) : par(N), rank(N) {
    REP(i, N) par[i] = i;
    REP(i, N) rank[i] = 0;
  }
  ~UnionFind() {}
  LL root(LL x) {
    if (par[x] == x)
      return x;
    else {
      par[x] = root(par[x]);
      return par[x];
    }
  }
  void unite(LL x, LL y) {
    LL rx = root(x);
    LL ry = root(y);
    if (rx == ry)
      return;
    if (rank[rx] < rank[ry]) {
      par[rx] = ry; // rankの高い方を親にする
    } else {
      par[ry] = rx;
      if (rank[rx] == rank[ry]) {
        // rankがどちらも同じ時、どちらか好きな方を親にしてそのrankを1上げる
        rank[rx]++;
      }
    }
  }
  bool same(LL x, LL y) {
    LL rx = root(x);
    LL ry = root(y);
    return rx == ry;
  }
};

//--------BFS---------

class BFS_shortestDistance {
public:
  BFS_shortestDistance(vector<vector<char>> p_, ll h_, ll w_) {
    p = p_;
    h = h_;
    w = w_;
    initial_number = h * w * 2;
    REP(i, h) {
      vector<LL> k(w);
      REP(t, w) k[t] = initial_number;
      field.push_back(k);
    }
  }
  vector<vector<char>> p;

  ll h;
  ll w;
  ll initial_number; // 初期化用数値

  vector<vector<LL>> field; // この変数に書き込む

  pair<LL, LL> plus(pair<LL, LL> &a, pair<LL, LL> &b) {
    pair<LL, LL> p;
    p.first = a.first + b.first;
    p.second = a.second + b.second;
    return p;
  }
  bool equal(pair<LL, LL> &a, pair<LL, LL> &b) {
    return (a.first == b.first && a.second == b.second);
  }
  bool is_in_field(int h, int w, const pair<LL, LL> &point) {
    const int c = point.second;
    const int r = point.first;
    return (0 <= c && c < w) && (0 <= r && r < h);
  }

  // fieldの中身を初期化
  // 最短距離がh*w*2になることはないのでこれで初期化する
  void init() {
    REP(i, field.size()) {
      REP(t, field[i].size()) { field[i][t] = initial_number; }
    }
  }

  // sy , sx はスタート位置の 『INDEX』!!
  // syが縦　sx が横
  void shortest(ll sy, ll sx) {
    // 初期化
    init();

    pair<LL, LL> c[4];
    c[0].first = 0;
    c[0].second = 1;
    c[1].first = 0;
    c[1].second = -1;
    c[2].first = 1;
    c[2].second = 0;
    c[3].first = -1;
    c[3].second = 0;
    queue<pair<LL, LL>> Q;
    pair<LL, LL> s;
    s.first = sy;
    s.second = sx;
    field[sy][sx] = 0; // スタート位置のみ0で初期化

    Q.push(s);
    while (Q.empty() == false) {
      pair<LL, LL> now = Q.front();
      Q.pop();

      for (int u = 0; u < 4; u++) {
        pair<LL, LL> x = c[u];
        pair<LL, LL> next = plus(now, x);
        if (is_in_field(h, w, next)) {
          if (p[next.first][next.second] == '.') {
            // まだ到達してない　＝＝　field の値が initial_number　
            if (field[next.first][next.second] == initial_number) {
              field[next.first][next.second] = field[now.first][now.second] + 1;
              Q.push(next);
            } else {
              // すでに到達済みである＝＝これ以前にQueueから出てきたpairがすでに
              // 到達している＝＝すでにfieldの値が最小値であることは明らか;
            }
          }
        }
      }
    }
  }
};

//-----------DP---------------//

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

//-----------MODつきCombination------------//
const int MAX = 1000007;
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;
}

//-------------bit全探索---------------

// aは空の二重配列
// aに格納する
void BIT(vector<vll> &a, ll n) {
  for (ll bit = 0; bit < (1 << n); bit++) {
    vll P;
    a.push_back(P);
    for (ll i = 0; i < n; i++) {
      if (bit & (1 << i)) {
        a[bit].push_back(i);
      }
    }
  }
}

// 桁数

int getdigit(ll n) { return log10(n) + 1; }

ll keta(ll n, ll k) {
  if (k > getdigit(n)) {
    return -1;
  } else if (k == 1) {
    return n % 10;
  } else {
    ll p = 1;
    REP(i, k) p *= 10;
    return (n % p) / (p / 10);
  }
}

//---------通常のnCr----------
long long nCr(int n, int r) {
  long long ans = 1;
  for (int i = n; i > n - r; --i) {
    ans = ans * i;
  }
  for (int i = 1; i < r + 1; ++i) {
    ans = ans / i;
  }
  return ans;
}

ll anti_division(ll a, ll b, ll n) {
  ll ans = 0;
  return ans;
}

//-----------MAIN------------//

vector<ll> seqence(vll x) { // xの連続してる部分をvectorにまとめる
  vll s;
  bool flag = 0; // 今連続しているかどうか
  ll before = x[0];
  ll seq = 0;
  REP(i, x.size()) {
    if (!flag && x[i] == before) {
      flag = 1;
      seq++;
      if (i == x.size() - 1) {
        s.push_back(seq);
      }
    } else if (flag && x[i] == before) {
      seq++;
      if (i == x.size() - 1) {
        s.push_back(seq);
      }
    } else if (flag && x[i] != before) {
      s.push_back(seq);
      seq = 1;
      flag = 0;
      // debug(i)
      if (i == x.size() - 1) {
        s.push_back(seq);
      }
    } else {
      s.push_back(seq);
      seq = 1;
      if (i == x.size() - 1) {
        s.push_back(seq);
      }
      flag = 0;
    }
    // debug(before)
    before = x[i];
  }
  return s;
}
ll kiriage(ll a, ll b) {
  if (b == 1)
    return a;
  if (a == 0)
    return 0;
  return a / b + (a % b == 0);
}

int main() {
  cout.precision(10);
  ll n, m, k, A, B;
  string s;
  map<ll, ll> p;
  vector<pll> Pairs;
  pll Ap;
  cin >> n >> m;
  vector<ll> a(n);
  REP(i, n) cin >> a[i];
  ll ind = MIN(a).second + 1;
  ll ans = 0;
  ans += kiriage((n - ind), m - 1) + kiriage(ind - 1, m - 1);

  if (n <= m)
    ans /= ans;
  cout << ans << endl;

  return 0;
}


Fixed submission:
// include
//------------------------------------------
#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
using namespace std;
// conversion
//------------------------------------------
inline int toInt(string s) {
  int v;
  istringstream sin(s);
  sin >> v;
  return v;
}
template <class T> inline string toString(T x) {
  ostringstream sout;
  sout << x;
  return sout.str();
}
// math
//-------------------------------------------
template <class T> inline T sqr(T x) { return x * x; }
// typedef
//------------------------------------------
typedef long long ll;
typedef long long LL;
typedef vector<long long> VLL;
typedef vector<long long> vll;
typedef pair<long long, long long> pll;
typedef pair<long long, long long> PLL;

// container util
//------------------------------------------
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define VECMAX(x) *max_element(ALL(x))
#define VECMIN(x) *min_element(ALL(x))
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i, c)                                                             \
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())
// repetition
//------------------------------------------
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)
#define MULTIPLE(i, n, k) for (int i = (k); i < (n); i += k + 1) // 倍数ループ
// constant
//------------------------------------------
const double EPS = 1e-10;
const double PI = acos(-1.0);
// clear memory
#define CLR(a) memset((a), 0, sizeof(a))
// debug
#define dump(x) cerr << #x << " = " << (x) << endl;
#define debug(x)                                                               \
  cerr << #x << " = " << (x) << " (L" << __LINE__ << ")"                       \
       << " " << __FILE__ << endl;
#define SIZEOF(x) sizeof(x) / sizeof(x[0])

const long long INF = 100000000000000;
const long long NINF = -100000000000000;

//----------------search for specific figure--------------------
//--------------------------------------------------------------

ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
ll nCr(ll n, ll r) {

  if (n == 0) {
    return 0;
  }
  if (r == 0) {
    return 1;
  }
  if (r == 1) {
    return n;
  }
  if (n == r) {
    return 1;
  }

  if (r > n / 2) {
    r = n / 2;
  }

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

// firstが最大値（最小値） , second が index
pair<LL, LL> maxP(vll a, ll size) {
  pair<ll, ll> p;
  vll::iterator iter = max_element(a.begin(), a.end());
  p.first = *iter;
  p.second = distance(a.begin(), iter);
  return p;
}

pair<LL, LL> minP(vll a, ll size) {
  pair<ll, ll> p;
  vll::iterator iter = min_element(a.begin(), a.end());
  p.first = *iter;
  p.second = distance(a.begin(), iter);
  return p;
}

ll sumL(vll a, ll size) {
  ll sum = 0;
  REP(i, size) { sum += a[i]; }
  return sum;
}

// aのなかにtがいくつあるか
ll counT(VLL a, ll t) {

  sort(a.begin(), a.end());
  return upper_bound(a.begin(), a.end(), t) -
         lower_bound(a.begin(), a.end(), t);
}

#define COUNT(a, b) counT((a), (b))
#define MAX(x) maxP(x, x.size())
#define MIN(x) minP(x, x.size())
#define SUM(x) sumL(x, x.size())

//-------------------DIVIDE----------------------
// DIV[i][j] は　i の j分割数 j == 0 && i != 0 なら 0
// 並び順を区別しない

ll DIV[1000 + 1][1000 + 1];
void divide(ll n, ll m) {
  DIV[0][0] = 1;
  FOR(i, 1, n + 1) { DIV[i][0] = 0; }
  REP(i, n + 1) { DIV[i][1] = 1; }
  FOR(i, 1, m + 1) {
    FOR(t, 0, n + 1) {
      if (DIV[t][i] > 0)
        continue;
      if (t >= i) {
        DIV[t][i] = DIV[t - i][i] + DIV[t][i - 1];
      } else {
        DIV[t][i] = DIV[t][i - 1];
      }
    }
  }
}
#define DIVIDE(a, b) (DIV[a][b] - DIV[a][(b)-1])

//-------要素を見つける-----------

ll search(vll &a, ll n) { // a内のnのindexを返す
  std::vector<ll>::iterator iter = std::find(a.begin(), a.end(), n);
  size_t index = distance(a.begin(), iter);
  return index;
}

//------------素数判定-----------------

//------------素数判定-----------------
vector<bool> IS_PRIME_CONTAINER(1000005, true);
// メモリを圧迫する可能性あり

void IsPrime_Contain(ll num) {
  IS_PRIME_CONTAINER[0] = false;
  IS_PRIME_CONTAINER[1] = false;
  FOR(i, 2, sqrt(num) + 1) {
    if (IS_PRIME_CONTAINER[i]) {
      FOR(j, 2, num / i + 1) {
        if (j * i <= num) {
          IS_PRIME_CONTAINER[i * j] = false;
        }
      }
    }
  }
}

inline bool IsPrime(ll num) { return IS_PRIME_CONTAINER[num]; }

//---------ベルマンフォード----------
struct E {
  ll from, to, cost;
};
ll DIST[100005];
// start と 辺の数 m 辺の情報 x を入力
void shortest(LL s, vector<E> &x, ll m) {
  REP(i, 100000) { DIST[i] = INF; }
  DIST[s] = 0;
  while (1) {
    bool t = false;
    REP(i, m) {
      E h = x[i];
      if (DIST[h.from] != INF && DIST[h.to] > DIST[h.from] + h.cost) {
        DIST[h.to] = DIST[h.from] + h.cost;
        t = true;
      }
    }
    if (!t) {
      break;
    }
  }
}

//----UnionFind-----

class UnionFind {
public:
  vll par;
  vll rank; // rankが高いほど上の親である
  UnionFind(LL N) : par(N), rank(N) {
    REP(i, N) par[i] = i;
    REP(i, N) rank[i] = 0;
  }
  ~UnionFind() {}
  LL root(LL x) {
    if (par[x] == x)
      return x;
    else {
      par[x] = root(par[x]);
      return par[x];
    }
  }
  void unite(LL x, LL y) {
    LL rx = root(x);
    LL ry = root(y);
    if (rx == ry)
      return;
    if (rank[rx] < rank[ry]) {
      par[rx] = ry; // rankの高い方を親にする
    } else {
      par[ry] = rx;
      if (rank[rx] == rank[ry]) {
        // rankがどちらも同じ時、どちらか好きな方を親にしてそのrankを1上げる
        rank[rx]++;
      }
    }
  }
  bool same(LL x, LL y) {
    LL rx = root(x);
    LL ry = root(y);
    return rx == ry;
  }
};

//--------BFS---------

class BFS_shortestDistance {
public:
  BFS_shortestDistance(vector<vector<char>> p_, ll h_, ll w_) {
    p = p_;
    h = h_;
    w = w_;
    initial_number = h * w * 2;
    REP(i, h) {
      vector<LL> k(w);
      REP(t, w) k[t] = initial_number;
      field.push_back(k);
    }
  }
  vector<vector<char>> p;

  ll h;
  ll w;
  ll initial_number; // 初期化用数値

  vector<vector<LL>> field; // この変数に書き込む

  pair<LL, LL> plus(pair<LL, LL> &a, pair<LL, LL> &b) {
    pair<LL, LL> p;
    p.first = a.first + b.first;
    p.second = a.second + b.second;
    return p;
  }
  bool equal(pair<LL, LL> &a, pair<LL, LL> &b) {
    return (a.first == b.first && a.second == b.second);
  }
  bool is_in_field(int h, int w, const pair<LL, LL> &point) {
    const int c = point.second;
    const int r = point.first;
    return (0 <= c && c < w) && (0 <= r && r < h);
  }

  // fieldの中身を初期化
  // 最短距離がh*w*2になることはないのでこれで初期化する
  void init() {
    REP(i, field.size()) {
      REP(t, field[i].size()) { field[i][t] = initial_number; }
    }
  }

  // sy , sx はスタート位置の 『INDEX』!!
  // syが縦　sx が横
  void shortest(ll sy, ll sx) {
    // 初期化
    init();

    pair<LL, LL> c[4];
    c[0].first = 0;
    c[0].second = 1;
    c[1].first = 0;
    c[1].second = -1;
    c[2].first = 1;
    c[2].second = 0;
    c[3].first = -1;
    c[3].second = 0;
    queue<pair<LL, LL>> Q;
    pair<LL, LL> s;
    s.first = sy;
    s.second = sx;
    field[sy][sx] = 0; // スタート位置のみ0で初期化

    Q.push(s);
    while (Q.empty() == false) {
      pair<LL, LL> now = Q.front();
      Q.pop();

      for (int u = 0; u < 4; u++) {
        pair<LL, LL> x = c[u];
        pair<LL, LL> next = plus(now, x);
        if (is_in_field(h, w, next)) {
          if (p[next.first][next.second] == '.') {
            // まだ到達してない　＝＝　field の値が initial_number　
            if (field[next.first][next.second] == initial_number) {
              field[next.first][next.second] = field[now.first][now.second] + 1;
              Q.push(next);
            } else {
              // すでに到達済みである＝＝これ以前にQueueから出てきたpairがすでに
              // 到達している＝＝すでにfieldの値が最小値であることは明らか;
            }
          }
        }
      }
    }
  }
};

//-----------DP---------------//

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

//-----------MODつきCombination------------//
const int MAX = 1000007;
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;
}

//-------------bit全探索---------------

// aは空の二重配列
// aに格納する
void BIT(vector<vll> &a, ll n) {
  for (ll bit = 0; bit < (1 << n); bit++) {
    vll P;
    a.push_back(P);
    for (ll i = 0; i < n; i++) {
      if (bit & (1 << i)) {
        a[bit].push_back(i);
      }
    }
  }
}

// 桁数

int getdigit(ll n) { return log10(n) + 1; }

ll keta(ll n, ll k) {
  if (k > getdigit(n)) {
    return -1;
  } else if (k == 1) {
    return n % 10;
  } else {
    ll p = 1;
    REP(i, k) p *= 10;
    return (n % p) / (p / 10);
  }
}

//---------通常のnCr----------
long long nCr(int n, int r) {
  long long ans = 1;
  for (int i = n; i > n - r; --i) {
    ans = ans * i;
  }
  for (int i = 1; i < r + 1; ++i) {
    ans = ans / i;
  }
  return ans;
}

ll anti_division(ll a, ll b, ll n) {
  ll ans = 0;
  return ans;
}

//-----------MAIN------------//

vector<ll> seqence(vll x) { // xの連続してる部分をvectorにまとめる
  vll s;
  bool flag = 0; // 今連続しているかどうか
  ll before = x[0];
  ll seq = 0;
  REP(i, x.size()) {
    if (!flag && x[i] == before) {
      flag = 1;
      seq++;
      if (i == x.size() - 1) {
        s.push_back(seq);
      }
    } else if (flag && x[i] == before) {
      seq++;
      if (i == x.size() - 1) {
        s.push_back(seq);
      }
    } else if (flag && x[i] != before) {
      s.push_back(seq);
      seq = 1;
      flag = 0;
      // debug(i)
      if (i == x.size() - 1) {
        s.push_back(seq);
      }
    } else {
      s.push_back(seq);
      seq = 1;
      if (i == x.size() - 1) {
        s.push_back(seq);
      }
      flag = 0;
    }
    // debug(before)
    before = x[i];
  }
  return s;
}
ll kiriage(ll a, ll b) {
  if (b == 1)
    return a;
  if (a == 0)
    return 0;
  return a / b + (a % b == 0);
}

int main() {
  cout.precision(10);
  ll n, m, k, A, B;
  string s;
  map<ll, ll> p;
  vector<pll> Pairs;
  pll Ap;
  cin >> n >> m;
  vector<ll> a(n);
  REP(i, n) cin >> a[i];
  ll ind = MIN(a).second + 1;
  ll ans = 0;
  ans += kiriage((n - ind), m - 1) + kiriage(ind - 1, m - 1);

  if (n <= m)
    ans /= ans;
  // cout << ans << endl;
  ll aa = 0;
  n -= m;
  aa++;
  while (n > 0) {
    n -= m - 1;
    aa++;
  }
  cout << aa << endl;
  return 0;
}