#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using ld = long double;

// #define int long long

#define pii pair<int, int>
#define pll pair<ld, ld>
#define vi vector<int>
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define mp make_pair
#define pb push_back
#define sz(v) (int)(v).size()
// #define endl '\n'

const ld eps = 1e-8;
const ll mod = 1e9 + 7;
const int inf0 = 1e9 + 10;
const ll inf = 2e18 + 10;

void solve();

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
#ifdef LC
    freopen("input.txt", "r", stdin);
    // freopen("output.txt", "w", stdout);
#endif
    cout << fixed << setprecision(20);
    int t = 1;
    //cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}

const int MAXN = 100;
const ld PI = atan2(0, -1);

ld dp[MAXN][MAXN][MAXN];

void solve() {
    int n;
    cin >> n;
    int p;
    cin >> p;
    vector<ld> a(n);
    for (int i = 0; i < n; ++i) cin >> a[i];
    for (int i = 0; i < n; ++i) {
        for (int d = 1; d < n; ++d) {
            int j = (i + d) % n;
            dp[0][i][j] = sinl((a[j] - a[i]) / 180 * PI) * 1e6;
            //cout << "dp[0][" << i << "][" << j << "] = " << dp[0][i][j] << "\n";
        }
    }
    for (int pins = 1; pins <= p - 2; ++pins) {
        for (int i = 0; i < n; ++i) {
            for (int d = pins + 1; d < n; ++d) {
                int j = (i + d) % n;
                dp[pins][i][j] = -100;
                for (int dk = pins; dk < d; ++dk) {
                    int k = (i + dk) % n;
                    dp[pins][i][j] = max(dp[pins][i][j], dp[pins - 1][i][k] + dp[0][k][j]);
                }
            }
        }
    }
    ld ans = 0;
    for (int i = 0; i < n; ++i) {
        for (int d = p - 2 + 1; d < n; ++d) {
            int j = (i + d) % n;
            ans = max(ans, dp[p - 2][i][j] + dp[0][j][i]);
        }
    }
    cout << ans / 2 << "\n";
}

// g++ -DLC -o a a.cpp && ./a