//  Nikita Golikov, 2023

#include <bits/stdc++.h>

using namespace std;

using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;

#ifdef GOLIKOV
  #include "/Users/golikovnik/contests/debug.h"
#else
  #define debug(...) ;
#endif

template <class A, class B>
bool smin(A& x, B&& y) {
  if (y < x) {
    x = y;
    return true;
  }
  return false;
}

template <class A, class B>
bool smax(A& x, B&& y) {
  if (x < y) {
    x = y;
    return true;
  }
  return false;
}

int main() {
#ifdef GOLIKOV
  assert(freopen("in", "rt", stdin));
  auto _clock_start = chrono::high_resolution_clock::now();
#endif
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  int n, p;
  cin >> n >> p;
  using ld = double;
  vector<ld> a(n);
  ld const pi = acos(-1.0);
  for (auto& x : a) {
    cin >> x;
    x /= 360;
    x *= 2 * pi;
  }
  vector score(n, vector<ld>(n));
  for (int i = 0; i < n; ++i) {
    for (int j = i + 1; j < n; ++j) {
      score[i][j] = sin(a[j] - a[i]);
      score[j][i] = sin(a[i] - a[j] + 2 * pi);
    }
  }
  ld ans = 0;

  ld const INF = -1e40;
  for (int s = 0; s < n; ++s) {
    vector dp(p + 1, vector<ld>(n + 1, INF));
    dp[1][s] = 0;
    for (int t = s + 1; t < n; ++t) {
      int fromCnt = min(p - 1, t - s);
      for (int cnt = fromCnt; cnt >= 1; --cnt) {
        for (int wh = s; wh < t; ++wh) {
          smax(dp[cnt + 1][t], dp[cnt][wh] + score[wh][t]);
        }
      }
    }
    for (int cnt = 3; cnt <= p; ++cnt) {
      for (int x = s + 1; x < n; ++x) {
        smax(ans, dp[cnt][x] + score[x][s]);
      }
    }
  }

  cout << setprecision(12) << fixed << ans * 500000 << '\n';

#ifdef GOLIKOV
  cerr << "Executed in " << chrono::duration_cast<chrono::milliseconds>(
      chrono::high_resolution_clock::now()
          - _clock_start).count() << "ms." << endl;
#endif
  return 0;
}