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#ifndef LOCAL
#pragma GCC optimize("O3")
#endif
#include <bits/stdc++.h>
#define FOR(i,p,k) for(int i=(p);i<=(k);++i)
#define REP(i,n) FOR(i,0,(n)-1)
#define RFOR(i,p,n) for(int i=(p);i>=(n);--i)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define ssize(x) int((x).size())
#define fi first
#define se second
#define V vector
#define pb push_back
#define eb emplace_back
#define C const
#define pn printf("\n")
using namespace std;
typedef long long ll;
typedef V<int> vi;
typedef V<ll> vll;
typedef const int ci;
typedef const ll cll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
void chmin(auto &a, auto b){a=min(a,b);}
void chmax(auto &a, auto b){a=max(a,b);}
ci inf = 2.1e9;
cll infll = 4.5e18;

typedef long double ld;
const ld eps = 1e-18;

int I(){
    int z;
    scanf("%d", &z);
    //cin >> z;
    return z;
}

void answer(){
    int n = I(), t = I();
    V<ld> wej(n);
    REP(i, n) scanf("%Lf", &wej[i]);
    sort(all(wej));
    reverse(all(wej));

    V<ld> dp(2*n+1, 0);
    V<ld> nowe(2*n+1, 0);
    dp[n] = 1;
    int poc = n, kon = n;// niezerowy przedział dp, nowe jest zawsze wyzerowane

    ld wyn = 0;
    auto ewal = [&](){
        ld suma = 0;
        FOR(i, max(poc, n+t), min(kon, 2*n)) suma += dp[i];
        chmax(wyn, suma);
    };

    ewal();
    for(ld p : wej){
        FOR(i, poc, kon){
            nowe[i+1] += p*dp[i];
            nowe[i-1] += (1-p)*dp[i];
            dp[i] = 0;
        }
        swap(dp, nowe);
        --poc, ++kon;
        while(dp[poc] < eps) dp[poc++] = 0;
        while(dp[kon] < eps) dp[kon--] = 0;
        ewal();
    }

    printf("%.15Lf\n", wyn);
}

int main(){
    //ios_base::sync_with_stdio(0);
    //cin.tie(0);
    int tt = 1;
    //tt = I();
    while(tt--) answer();
}