// poj3744
#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<cmath>
#define LL long long
#define inf 1<<30
#define eps 1e-8
#define Pi acos(-1.0)
#define free(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);
using namespace std;

double tmp[2][2],f[2][2],t[2][2],p;
int a[20],n;

void power(int k) {
	t[0][0]=p,t[0][1]=1,t[1][0]=1-p,t[1][1]=0;
	while (k) {
		if (k&1) {
			for (int i=0;i<=1;i++)
				for (int j=0;j<=1;j++) {
					tmp[i][j]=0;
					for (int k=0;k<=1;k++) tmp[i][j]+=f[i][k]*t[k][j];
				}
			memcpy(f,tmp,sizeof(f));
		}
		k>>=1;
		for (int i=0;i<=1;i++)
			for (int j=0;j<=1;j++) {
				tmp[i][j]=0;
				for (int k=0;k<=1;k++) tmp[i][j]+=t[i][k]*t[k][j];
			}
		memcpy(t,tmp,sizeof(t));
	}
}
int main() {
	while (scanf("%d%lf",&n,&p)!=EOF) {
		for (int i=1;i<=n;i++) scanf("%d",&a[i]);
		sort(a+1,a+1+n);a[0]=0;
		f[1][1]=1;
		for (int i=1;i<=n;i++) {
			f[1][0]=f[1][1]*p;
			f[0][1]=f[1][0]*p+f[1][1]*(1-p);
			f[0][0]=f[0][1]*p+f[1][0]*(1-p);
			if (a[i]-a[i-1]==1) {f[1][1]=0;break;}
			else if (a[i]-a[i-1]==2) f[1][1]=f[1][1]*(1-p);
			else if (a[i]-a[i-1]==3) f[1][1]=f[1][0]*(1-p);
			else if (a[i]-a[i-1]==4) f[1][1]=f[0][1]*(1-p);
			else power(a[i]-a[i-1]-5),f[1][1]=(1-p)*f[0][0];
		}
		if (fabs(f[1][1])<eps) puts("0.0000000");
		else printf("%.7lf\n",f[1][1]);
	}
	return 0;
}