include Math
n=gets.to_i
l=(0..n+1).map{gets.to_f}
k=l[0]
f=->(r,s){r-s>k ?PI*s*s:s-r>k ?PI*r*r:r+s<k ?0:(x=(k*k+r*r-s*s)/2/k;h=sqrt(r*r-x*x);r*r*atan2(h,x)+s*s*atan2(h,k-x)-k*h)}
1.upto(n){|i|e=l[1..i];b=e.sum;a=[e.max*2-b,0].max;e=l[i+1..n+1];d=e.sum;c=[e.max*2-d,0].max;p f[a,c]-f[a,d]-f[b,c]+f[b,d]}