#include<cstdio>

 #include<cstring>

 #include<string>

 #include<cmath>

 #include<iostream>

 #include<algorithm>

 #include<map>

 #include<set>

 #include<queue>

 #include<vector>

 using namespace std;

 typedef long long ll;

 typedef unsigned int uint;

 typedef unsigned long long ull;

 typedef pair<int,int> PII;

 typedef vector<int> VI;

 #define fi first

 #define se second

 #define MP make_pair

 #define N   1100000

 #define MOD 1000000007

 #define eps 1e-8

 #define pi  acos(-1)

 int n;

 double L;

 int read()

 {

    int v=,f=;

    char c=getchar();

    while(c<||<c) {if(c=='-') f=-; c=getchar();}

    while(<=c&&c<=) v=(v<<)+v+v+c-,c=getchar();

    return v*f;

 }

 int main()

 {

     while(scanf("%d%lf",&n,&L)!=EOF)

     {

          double ans=;

          for(int i = ; i <= n; ++i)

          {

              double x;

              scanf("%lf",&x);

              x/=*1.0;

              x*=pi*1.0;

              ans+=1.0/*L*L*sin(x);

          }

          printf("%.3lf\n",ans);

     }

     return ;

 }