#include<bits/stdc++.h>
#define int long long
using namespace std;
#define fi first
#define se second
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define per(i,a,b) for(int i=(a);i>=(b);i--)
#define eb emplace_back
#define y1 yylyylyylyyl
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pii> vp;
typedef unsigned long long ull;
 
long long read() {
    long long res=0, w=1; char c=getchar();
    while(!isdigit(c)) {if(c=='-') w=-1; c=getchar();}
    while(isdigit(c)) {res=res*10+c-48, c=getchar();}
    return res*w;
}

const int N=5009;
int n,m;
double p[N],f[N][N<<1],g[N];

signed main() {
    n=read(), m=read();
    rep(i,1,n) scanf("%lf",&p[i]);
    sort(p+1,p+n+1,greater<double>());
    int base=n;
    f[0][base]=1;
    rep(i,1,n) {
        rep(j,base-i+1,base+i-1) {
            f[i][j-1]+=f[i-1][j]*(1-p[i]);
            f[i][j+1]+=f[i-1][j]*p[i];
        }
        rep(j,base+m,base+i) g[i]+=f[i][j];
    }
    double ans=0;
    rep(i,1,n) ans=max(ans,g[i]);
    printf("%.8lf\n",ans);
    return 0;
}