#include <bits/stdc++.h>   using namespace std;   double p[105];   double a[205][205], b[205][205];   int main(void) {     int n;     scanf( %d , &n);     for (int i = 0; i <= n; i++) {       scanf( %lf , &p[i]);     }     for (int i = 0; i <= 2 * n; i++)       for (int j = 0; j <= 2 * n; j++) a[i][j] = -100;     for (int i = 0; i <= 2 * n; i++)       for (int j = 0; j <= i && j <= n; j++) {         int ni = n + i - j - j;         a[i][ni] = p[j];       }     for (int t = 0; t <= 30; t++) {       for (int i = 0; i <= 2 * n; i++)         for (int j = 0; j <= 2 * n; j++) b[i][j] = -100;       for (int i = 0; i <= 2 * n; i++)         for (int j = 0; j <= 2 * n; j++)           for (int k = 0; k <= 2 * n; k++) {             double t = a[i][k] + a[k][j];             if (t > b[i][j]) b[i][j] = t;           }       for (int i = 0; i <= 2 * n; i++)         for (int j = 0; j <= 2 * n; j++)           if (b[i][j] < 0)             a[i][j] = -100;           else             a[i][j] = b[i][j] / 2;     }     double res = 0.0;     for (int i = 0; i <= 2 * n; i++)       for (int j = 0; j <= 2 * n; j++) res = max(a[i][j], res);     printf( %.20lf n , res);     return 0;   }   