#include<bits/stdc++.h>
#define int long long
using namespace std;
namespace IO{
	template<typename T> inline void read(T &x){
		bool f=1;x=0;char ch=getchar();
		while(ch<'0'||ch>'9'){if(ch=='-')f=0;ch=getchar();}
		while(ch>='0'&&ch<='9')x=(x<<1)+(x<<3)+(ch&15),ch=getchar();
		x=f?x:-x;
	}
	template<typename T> inline void write(T x){
		if(x<0) putchar('-'),x=-x;
	   	if(x>9) write(x/10);
	   	putchar(('0'+x%10));
	}
	template <typename T,typename ...Args> inline void read(T &x,Args &...args){read(x);read(args...);}
	template<typename T> inline void write(T x,char c){write(x),putchar(c);}
}
using namespace IO;
double p[1010],f[1010];
int n,m,k;
signed main(){
	read(n,m);
	for(int i=0;i<n;i++)scanf("%lf",&p[i]);
	f[1]=p[0];
	for(int i=2;i<=m;++i){
		f[i]=p[0];
		for(int j=1;j<n;++j)f[i]+=p[j]*pow(f[i-1],j);
	}
	printf("%0.4lf",f[m]);
	return 0;
}