#include<bits/stdc++.h>
using namespace std;
int n,m;
long double p[301],ans[301];
long double fpow(long double a,int b){
	long double ret=1;
	while(b){
		if(b&1)ret*=a;
		a*=a;
		b>>=1;
	}
	return ret;
}
long double dfs(int h){
	if(h<1)return 0;
	if(h==1)return p[0];
	if(ans[h]!=0)return ans[h];
	long double pos=p[0];
	for(int i=1;i<n;i++){
		pos+=p[i]*fpow(dfs(h-1),i);
		//cout<<pos<<" ";
	}
	//out<<endl;
	return pos;
}
int main(){
	cin >> n >> m;
	for(int i=0;i<n;i++){
		cin >> p[i];
		//cout<<p[i]<<" ";
	}
	memset(ans,0,sizeof(ans));
	long double ret=dfs(m);
	ret*=10000;
	ret=floor(ret);
	ret/=10000;
	cout<<ret<<endl; 
	return 0;
}