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// Witold Milewski
// PA 2025
#include <bits/stdc++.h>
#define int long long
using namespace std;
#define FOR(i, a, b) for(int i=a; i<=b; ++i)
#define FORB(i, b, a) for(int i=b; i>=a; --i)
#define sz(A) (int)(A.size())
#define ll long long
#define ld long double
#define eb emplace_back
#define pb push_back
#define pi pair<int, int>
#define f first
#define s second
#define rs resize
#define V vector

const int maxn=50007, offset=50000;
ld dp[2][2*maxn];

int n, t;

signed main() {
  cin >> n >> t;
  V<ld> praw;
  ld x;
  FOR(i, 1, n) {
    cin >> x;
    praw.eb(x);
  }
  sort(praw.begin(), praw.end(), greater<ld>());

  FOR(i, 0, 1) FOR(j, 0, maxn-1) dp[i][j]=0;
  dp[0][offset+0]=1;
  ld wyn=0;
  FOR(i, 0, sz(praw)-1) {
    ld p = praw[i];
    int a = i%2;
    int b = 1-a;
    FOR(j, 0, 2*maxn-1) dp[b][j]=0;
    FOR(j, 1, 2*maxn-2) {
      dp[b][j+1]+=dp[a][j]*p;
      dp[b][j-1]+=dp[a][j]*(1.0-p);
    }

    ld praw = 0;
    FOR(j, t, maxn-1) praw+=dp[b][offset+j];
    // if(i%2==0) cout << fixed << setprecision(7) << praw << '\n';
    wyn=max(wyn, praw);
  }
  cout << fixed << setprecision(7) << wyn << '\n';
}