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 #include <iostream>
#include <algorithm>
using namespace std;
const int maxn=12;
int n;
double p;
struct matrix
   {
 double m[2][2];
 };
int mine[maxn];
matrix operator*(const matrix&a,const matrix&b)
{
matrix tmp;
int i,j,k;
for(i=0;i<2;i++)
for(j=0;j<2;j++)
  {
tmp.m[i][j]=0;
for(k=0;k<2;k++)
tmp.m[i][j]+=a.m[i][k]*b.m[k][j];
 }
return tmp;
}
matrix power(int k)
{
matrix tmp,res;
matrix A;
A.m[0][0]=p,A.m[0][1]=1-p,A.m[1][0]=1,A.m[1][1]=0;
matrix B;
B.m[0][0]=1,B.m[0][1]=0,B.m[1][0]=0,B.m[1][1]=1;
if(k==0)
return B;
if(k==1)
return A;
else
{
tmp=power(k/2);
res=tmp*tmp;
if(k%2==1)
res=res*A;
return res;
}
}
void slove(int n,double p)
{
double a=1,b=0;
int i;
for(i=0;i<n;i++)
scanf("%d",&mine[i]);
sort(mine,mine+n);
double f2=1.0,f1=0.0;
int now=1;
for(i=0;i<n;i++)
{
if((mine[i]-1)-now>=0)
{
matrix tmp=power(mine[i]-1-now);
f2=(tmp.m[0][0]*f2+tmp.m[0][1]*f1)*(1-p);
f1=0;
now=mine[i]+1;
}
else
{
printf("%.7lf\n",0.0);
return;
}
}
printf("%.7lf\n",f2);
}
int main()
{
while(scanf("%d %lf",&n,&p)!=EOF)
slove(n,p);
return 0;
}
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