Problem p02780 (C++)

Buggy submission (status: Time Limit Exceeded):
/*                                  / \ (Hello)//JSM//*/
/*                                 /*****\ */
/*     Jai Shree Mataji           /       \ |\| |_| $ |-| K */
#include <algorithm>
#include <bits/stdc++.h>
#include <cmath>
#include <cstring>
#include <iostream>
#include <map>
#include <set>
#include <string.h>
#include <vector>
using namespace std;
#define ll long long int
#define ld long double
#define MOD 1000000007
#define PI 3.1415926535897932384626433832795
#define YY cout << "YES"
#define NN cout << "NO"
#define EE cout << "\n"
#define ee cout << "\n"
#define ne cout << "-1"
#define pb push_back
#define fi first
#define se second
#define mkp make_pair
#define mkt make_tuple
#define sall(v) sort(v.begin(), v.end())
#define all(v) v.begin(), v.end()
#define fo(i, n) for (ll i = 0; i < n; i++)
#define vl vector<ll>
#define vc vector<char>
#define vll vector<pair<ll, ll>>
#define mps map<string, ll>
#define mpc map<char, ll>
#define mpl map<ll, ll>
#define pr pair<ll, ll>
#define tpl tuple<ll, ll, ll>
bool sortbysec(const pair<int, int> &a, const pair<int, int> &b) {
  return (a.second < b.second);
}
ll containsDigit(ll number, ll digit) {
  while (number != 0) {
    int curr_digit = number % 10;
    if (curr_digit == digit)
      return 1;
    number /= 10;
  }
  return 0;
}
ll soltn(ll x, ll n) {
  if (x >= 0)
    return x % n;
  else
    return n + x % n;
}
ll bin_srch(ll L[], ll N, ll item) {
  ll flag = -2;
  int l = 0, u = N - 1, m;
  while (l <= u) {
    m = (l + u) / 2;
    if (item == L[m]) {
      flag = m - 1;
      break;
    } else if (item > L[m])
      l = m - 1;
    else
      u = m + 1;
  }
  return flag;
}
ll pd(ll x, ll y) {
  if (x % y == 0)
    return x / y;
  else
    return x / y + 1;
}
ll coda(ll n, ll d) {
  ll count = 0;
  while (n != 0) {
    if (n % 10 == d)
      count++;
    n /= 10;
  }
  return count;
}
ll minDissame(ll a[], ll n) {
  map<ll, ll> hmap;
  ll minDistance = INT_MAX;
  ll previousIndex = 0, currentIndex = 0;
  for (ll i = 0; i < n; i++) {
    if (hmap.find(a[i]) != hmap.end()) {
      currentIndex = i;
      previousIndex = hmap[a[i]];
      minDistance = min((currentIndex - previousIndex), minDistance);
    }
    hmap[a[i]] = i;
  }
  return (minDistance == INT_MAX ? -1 : minDistance);
}
ll minDistanytwo(ll arr[], ll n, ll x, ll y) {
  ll p = -1, min_dist = INT_MAX;
  for (ll i = 0; i < n; i++) {
    if (arr[i] == x || arr[i] == y) {
      if (p != -1 && arr[i] != arr[p])
        min_dist = min(min_dist, i - p);
      p = i;
    }
  }
  if (min_dist == INT_MAX)
    return -1;
  return min_dist;
}
ll mdls(ll x) { return max(x, -x); }
ll pow1(ll n, ll p) {
  if (p == 0)
    return 1;
  ll x = pow1(n, p / 2);
  x = (x * x);
  if (p % 2 == 0)
    return x;
  else
    return (x * n);
}
string fumn(string s) {
  string p;
  for (ll i = 0; i < s.length(); i++)
    if (isalpha(s[i]))
      p += toupper(s[i]);
  return p;
}
ll turns(string S, string SS) {
  ll i, cc = 0, l = S.length();
  fo(i, l) {
    if (S[i] != SS[i])
      cc++;
  }
  return cc / 2;
}
ll isSubstr(string s1, string s2) {
  ll M = s1.length();
  ll N = s2.length();
  for (ll i = 0; i <= N - M; i++) {
    ll j;
    for (j = 0; j < M; j++)
      if (s2[i + j] != s1[j])
        break;
    if (j == M)
      return i;
  }
  return -1;
}
// s2>s1;if(not) rtrn -1;
ll hhh2(unsigned ll n) {
  if (n < 1)
    return 0;
  ll res = 1;
  ll u = 0;
  for (ll i = 0; i < 8 * sizeof(unsigned ll); i++) {
    ll curr = 1 << i;
    if (curr > n)
      break;
    u++;
    res = curr;
  }
  return u;
}
ld ldgcd(ld a, ld b) { return a < 0.0001 ? b : ldgcd(fmod(b, a), a); }
void onesol(ll a, ll b, ll &x, ll &y, ll &g) {
  if (!b) {
    g = a;
    x = 1;
    y = 0;
  } else {
    onesol(b, a % b, y, x, g);
    y -= a / b * x;
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  ll tt = 1;
  //	      cin>>tt;
  while (tt--) {
    /*
    5 3
    1 2 2 4 5*/
    ll n, m, j, k, l, i;
    cin >> n >> m;
    ld a[n];
    fo(i, n) cin >> a[i];
    ld s = 0;
    ld mi = 0;
    fo(i, n - (m - 1)) {
      s = 0;
      fo(j, m) {
        s += a[j + i];
        s++;
      }
      mi = max(s, mi);
    }
    cout << fixed << setprecision(10) << mi / 2;
    ee;
  }
  return 0;
}


Fixed submission:
/*                                  / \ (Hello)//JSM//*/
/*                                 /*****\ */
/*     Jai Shree Mataji           /       \ |\| |_| $ |-| K */
#include <algorithm>
#include <bits/stdc++.h>
#include <cmath>
#include <cstring>
#include <iostream>
#include <map>
#include <set>
#include <string.h>
#include <vector>
using namespace std;
#define ll long long int
#define ld long double
#define MOD 1000000007
#define PI 3.1415926535897932384626433832795
#define YY cout << "YES"
#define NN cout << "NO"
#define EE cout << "\n"
#define ee cout << "\n"
#define ne cout << "-1"
#define pb push_back
#define fi first
#define se second
#define mkp make_pair
#define mkt make_tuple
#define sall(v) sort(v.begin(), v.end())
#define all(v) v.begin(), v.end()
#define fo(i, n) for (ll i = 0; i < n; i++)
#define vl vector<ll>
#define vc vector<char>
#define vll vector<pair<ll, ll>>
#define mps map<string, ll>
#define mpc map<char, ll>
#define mpl map<ll, ll>
#define pr pair<ll, ll>
#define tpl tuple<ll, ll, ll>
bool sortbysec(const pair<int, int> &a, const pair<int, int> &b) {
  return (a.second < b.second);
}
ll containsDigit(ll number, ll digit) {
  while (number != 0) {
    int curr_digit = number % 10;
    if (curr_digit == digit)
      return 1;
    number /= 10;
  }
  return 0;
}
ll soltn(ll x, ll n) {
  if (x >= 0)
    return x % n;
  else
    return n + x % n;
}
ll bin_srch(ll L[], ll N, ll item) {
  ll flag = -2;
  int l = 0, u = N - 1, m;
  while (l <= u) {
    m = (l + u) / 2;
    if (item == L[m]) {
      flag = m - 1;
      break;
    } else if (item > L[m])
      l = m - 1;
    else
      u = m + 1;
  }
  return flag;
}
ll pd(ll x, ll y) {
  if (x % y == 0)
    return x / y;
  else
    return x / y + 1;
}
ll coda(ll n, ll d) {
  ll count = 0;
  while (n != 0) {
    if (n % 10 == d)
      count++;
    n /= 10;
  }
  return count;
}
ll minDissame(ll a[], ll n) {
  map<ll, ll> hmap;
  ll minDistance = INT_MAX;
  ll previousIndex = 0, currentIndex = 0;
  for (ll i = 0; i < n; i++) {
    if (hmap.find(a[i]) != hmap.end()) {
      currentIndex = i;
      previousIndex = hmap[a[i]];
      minDistance = min((currentIndex - previousIndex), minDistance);
    }
    hmap[a[i]] = i;
  }
  return (minDistance == INT_MAX ? -1 : minDistance);
}
ll minDistanytwo(ll arr[], ll n, ll x, ll y) {
  ll p = -1, min_dist = INT_MAX;
  for (ll i = 0; i < n; i++) {
    if (arr[i] == x || arr[i] == y) {
      if (p != -1 && arr[i] != arr[p])
        min_dist = min(min_dist, i - p);
      p = i;
    }
  }
  if (min_dist == INT_MAX)
    return -1;
  return min_dist;
}
ll mdls(ll x) { return max(x, -x); }
ll pow1(ll n, ll p) {
  if (p == 0)
    return 1;
  ll x = pow1(n, p / 2);
  x = (x * x);
  if (p % 2 == 0)
    return x;
  else
    return (x * n);
}
string fumn(string s) {
  string p;
  for (ll i = 0; i < s.length(); i++)
    if (isalpha(s[i]))
      p += toupper(s[i]);
  return p;
}
ll turns(string S, string SS) {
  ll i, cc = 0, l = S.length();
  fo(i, l) {
    if (S[i] != SS[i])
      cc++;
  }
  return cc / 2;
}
ll isSubstr(string s1, string s2) {
  ll M = s1.length();
  ll N = s2.length();
  for (ll i = 0; i <= N - M; i++) {
    ll j;
    for (j = 0; j < M; j++)
      if (s2[i + j] != s1[j])
        break;
    if (j == M)
      return i;
  }
  return -1;
}
// s2>s1;if(not) rtrn -1;
ll hhh2(unsigned ll n) {
  if (n < 1)
    return 0;
  ll res = 1;
  ll u = 0;
  for (ll i = 0; i < 8 * sizeof(unsigned ll); i++) {
    ll curr = 1 << i;
    if (curr > n)
      break;
    u++;
    res = curr;
  }
  return u;
}
ld ldgcd(ld a, ld b) { return a < 0.0001 ? b : ldgcd(fmod(b, a), a); }
void onesol(ll a, ll b, ll &x, ll &y, ll &g) {
  if (!b) {
    g = a;
    x = 1;
    y = 0;
  } else {
    onesol(b, a % b, y, x, g);
    y -= a / b * x;
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  ll tt = 1;
  //	      cin>>tt;
  while (tt--) {
    /*
    5 3
    1 2 2 4 5*/
    ll n, m, j, k, l, i;
    cin >> n >> m;
    ld a[n];
    fo(i, n) cin >> a[i];
    ld s = 0;
    ld mi = 0;
    fo(i, m) mi += a[i];
    s = mi + m;
    mi += m;
    fo(i, n + 1 - m) {
      s += a[m + i] - a[i];
      mi = max(mi, s);
    }
    cout << fixed << setprecision(10) << mi / 2;
    ee;
  }
  return 0;
}