1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
#include <cstdio>
#include <vector>
#include <algorithm>
#include <cmath>

#define MAXN 50009
#define WIDTH 2
std::vector<double> P;
double SMEM[MAXN][WIDTH];
int n, t;

/* Stn */
#define S(tt, nn) (SMEM[tt][(nn) % WIDTH])

void dump_mem()
{
    for (int i = 0; i < WIDTH; ++i) {
        for (int j = 0; j <= t; ++j)
            printf(" %lf", S(j, i));
        printf("\n");
    }
}

struct myclass {
    bool operator() (double i, double j) { return (i > j);}
} sorter;
  
double egzamin()
{
    std::sort(P.begin(), P.end(), sorter);

    S(0, 1) = 1;
    S(1, 1) = P[0];

    double best = 0;
    for (int i = 2; i <= n; ++i) {
        int tp = ceil(double(t + i) / 2);

        S(0, i) = 1;
        for (int j = 1; j <= n; ++j) {
            S(j, i) = P[i - 1] * S(j - 1, i - 1) + (1 - P[i - 1]) * S(j, i - 1);
        }

        if (S(tp, i) > best)
            best = S(tp, i);
    }

    return best;
}

int main()
{
    scanf("%d%d", &n, &t);
    P.resize(n);
    for (int i = 0; i < n; ++i)
        scanf("%lf", &P[i]);

    printf("%.9lf\n", egzamin());
    return 0;
}