#include <iostream>

 #include <cstdlib>

 #include <cstring>

 #include <cstdio>

 #include <cmath>

 #include <algorithm>

 using namespace std;

 typedef double LF;

 const LF Eps = 1e-;

 inline LF gmin(LF a, LF b) {return a < b ? a : b;}

 inline LF gmax(LF a, LF b) {return a > b ? a : b;}

 inline LF Sqr(LF x) {return x * x;}

 const int MaxN =  + ;

 int n;

 LF Alpha, talpha, Ht, Lp, Rp, Ans;

 LF A[MaxN], P[MaxN], Rad[MaxN], Ls[MaxN], Rs[MaxN], Lh[MaxN], Rh[MaxN];

 inline LF f(LF x)

 {

     LF ret = 0.0;

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

     {

         if (fabs(x - P[i]) < Rad[i]) ret = gmax(ret, sqrt(Sqr(Rad[i]) - Sqr(x - P[i])));

         if (x > Ls[i] && x < Rs[i]) ret = gmax(ret, Lh[i] + (Rh[i] - Lh[i]) * (x - Ls[i]) / (Rs[i] - Ls[i]));

     }

     return ret;

 }

 inline LF Simpson(LF l, LF r, LF fl, LF fmid, LF fr)

 {

     return (fl + fmid * 4.0 + fr) / 6.0 * (r - l);

 }

 LF RSimpson(LF l, LF r, LF fl, LF fmid, LF fr)

 {

     LF mid, p, q, x, y, z;

     mid = (l + r) / 2.0;

     p = f((l + mid) / 2.0);

     q = f((mid + r) / 2.0);

     x = Simpson(l, r, fl, fmid, fr);

     y = Simpson(l, mid, fl, p, fmid);

     z = Simpson(mid, r, fmid, q, fr);

     if (fabs(x - y - z) < Eps) return y + z;

     else return RSimpson(l, mid, fl, p, fmid) + RSimpson(mid, r, fmid, q, fr);

 }

 int main()

 {

     scanf("%d%lf", &n, &Alpha);

     talpha = tan(Alpha);

     Ht = 0.0;

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

     {

         scanf("%lf", &A[i]);

         Ht += A[i];

         P[i] = Ht / talpha;

     }

     Lp = P[]; Rp = P[n + ];

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

     {

         scanf("%lf", &Rad[i]);

         Lp = gmin(Lp, P[i] - Rad[i]);

         Rp = gmax(Rp, P[i] + Rad[i]);

     }

     Rad[n + ] = 0.0;

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

     {

         if (P[i + ] - P[i] > fabs(Rad[i + ] - Rad[i]))

         {

             Ls[i] = P[i] + Rad[i] * (Rad[i] - Rad[i + ]) / (P[i + ] - P[i]);

             Rs[i] = P[i + ] + Rad[i + ] * (Rad[i] - Rad[i + ]) / (P[i + ] - P[i]);

             Lh[i] = sqrt(Sqr(Rad[i]) - Sqr(Ls[i] - P[i]));

             Rh[i] = sqrt(Sqr(Rad[i + ]) - Sqr(Rs[i] - P[i + ]));

         }

         else

         {

             Ls[i] = -;

             Rs[i] = -;

         }

     }

     Ans = RSimpson(Lp, Rp, f(Lp), f((Lp + Rp) / 2.0), f(Rp)) * ;

     printf("%.2lf\n", Ans);

     return ;

 }