#pragma GCC optimize ("Ofast")
#include<bits/stdc++.h>
using namespace std;
inline int my_getchar_unlocked(){
  static char buf[1048576];
  static int s = 1048576;
  static int e = 1048576;
  if(s == e && e == 1048576){
    e = fread_unlocked(buf, 1, 1048576, stdin);
    s = 0;
  }
  if(s == e){
    return EOF;
  }
  return buf[s++];
}
inline void rd(int &x){
  int k;
  int m=0;
  x=0;
  for(;;){
    k = my_getchar_unlocked();
    if(k=='-'){
      m=1;
      break;
    }
    if('0'<=k&&k<='9'){
      x=k-'0';
      break;
    }
  }
  for(;;){
    k = my_getchar_unlocked();
    if(k<'0'||k>'9'){
      break;
    }
    x=x*10+k-'0';
  }
  if(m){
    x=-x;
  }
}
struct MY_WRITER{
  char buf[1048576];
  int s;
  int e;
  MY_WRITER(){
    s = 0;
    e = 1048576;
  }
  ~MY_WRITER(){
    if(s){
      fwrite_unlocked(buf, 1, s, stdout);
    }
  }
}
;
MY_WRITER MY_WRITER_VAR;
void my_putchar_unlocked(int a){
  if(MY_WRITER_VAR.s == MY_WRITER_VAR.e){
    fwrite_unlocked(MY_WRITER_VAR.buf, 1, MY_WRITER_VAR.s, stdout);
    MY_WRITER_VAR.s = 0;
  }
  MY_WRITER_VAR.buf[MY_WRITER_VAR.s++] = a;
}
inline void wt_L(char a){
  my_putchar_unlocked(a);
}
int WRITER_DOUBLE_DIGIT = 15;
inline int writerDigit_double(){
  return WRITER_DOUBLE_DIGIT;
}
inline void writerDigit_double(int d){
  WRITER_DOUBLE_DIGIT = d;
}
inline void wt_L(double x){
  const int d = WRITER_DOUBLE_DIGIT;
  int k;
  int r;
  double v;
  if(x!=x || (x==x+1 && x==2*x)){
    my_putchar_unlocked('E');
    my_putchar_unlocked('r');
    my_putchar_unlocked('r');
    return;
  }
  if(x < 0){
    my_putchar_unlocked('-');
    x = -x;
  }
  x += 0.5 * pow(0.1, d);
  r = 0;
  v = 1;
  while(x >= 10*v){
    v *= 10;
    r++;
  }
  while(r >= 0){
    r--;
    k = floor(x / v);
    if(k >= 10){
      k = 9;
    }
    if(k <= -1){
      k = 0;
    }
    x -= k * v;
    v *= 0.1;
    my_putchar_unlocked(k + '0');
  }
  if(d > 0){
    my_putchar_unlocked('.');
    v = 1;
    for(r=(0);r<(d);r++){
      v *= 0.1;
      k = floor(x / v);
      if(k >= 10){
        k = 9;
      }
      if(k <= -1){
        k = 0;
      }
      x -= k * v;
      my_putchar_unlocked(k + '0');
    }
  }
}
template<class T, class S, class U> inline void DigitF_L(T n, int sz, S res[], U b){
  int i;
  for(i=(0);i<(sz);i++){
    res[i] = n % b;
    n /= b;
  }
}
template<class S, class T> inline S chmax(S &a, T b){
  if(a<b){
    a=b;
  }
  return a;
}
int N;
int A[10];
double dp[2][59049];
int arr[10];
int pw[11];
int main(){
  int ao_dF3pO, i, mask;
  int s1;
  int s2;
  double tmp;
  pw[0] = 1;
  for(i=(0);i<(10);i++){
    pw[i+1] = pw[i] * 3;
  }
  rd(N);
  {
    int Q5VJL1cS;
    for(Q5VJL1cS=(0);Q5VJL1cS<(N);Q5VJL1cS++){
      rd(A[Q5VJL1cS]);
    }
  }
  for(mask=(0);mask<(pw[N]);mask++){
    DigitF_L(mask, N, arr, 3);
    for(i=(0);i<(N);i++){
      if(arr[i]==0){
        break;
      }
    }
    if(i < N){
      continue;
    }
    s1 = s2 = 0;
    for(i=(0);i<(N);i++){
      if(arr[i]==1){
        s1+= A[i];
      }
      else{
        s2+= A[i];
      }
    }
    if(s1 > s2){
      dp[0][mask] = 1;
    }
    else{
      dp[1][mask] = 1;
    }
  }
  for(ao_dF3pO=(0);ao_dF3pO<(400);ao_dF3pO++){
    int p;
    for(p=(0);p<(2);p++){
      for(mask=(0);mask<(pw[N]);mask++){
        DigitF_L(mask, N, arr, 3);
        for(i=(0);i<(N);i++){
          if(arr[i]==0){
            break;
          }
        }
        if(i==N){
          continue;
        }
        dp[p][mask] = 0;
        for(i=(0);i<(N);i++){
          if(arr[i]==0){
            tmp = 0;
            tmp += (1.0 / A[i]) * (1 - dp[p^1][mask + pw[i] * (p+1)]);
            tmp += (1 - 1.0 / A[i]) * (1 - dp[p^1][mask]);
            chmax(dp[p][mask], tmp);
          }
        }
      }
    }
  }
  wt_L(dp[0][0]);
  wt_L('\n');
  return 0;
}
// cLay varsion 20200509-1

// --- original code ---
// int N, A[10];
// double dp[2][59049];
// int arr[10], pw[11];
// {
//   int s1, s2;
//   double tmp;
// 
//   pw[0] = 1;
//   rep(i,10) pw[i+1] = pw[i] * 3;
// 
//   rd(N,A(N));
// 
//   rep(mask,pw[N]){
//     DigitF(mask, N, arr, 3);
//     rep(i,N) if(arr[i]==0) break;
//     if(i < N) continue;
// 
//     s1 = s2 = 0;
//     rep(i,N) if[arr[i]==1, s1, s2] += A[i];
//     dp[if[s1 > s2, 0, 1]][mask] = 1;
//   }
// 
//   rep(400){
//     rep(p,2) rep(mask,pw[N]){
//       DigitF(mask, N, arr, 3);
//       rep(i,N) if(arr[i]==0) break;
//       if(i==N) continue;
// 
//       dp[p][mask] = 0;
//       rep(i,N) if(arr[i]==0){
//         tmp = 0;
//         tmp += (1.0 / A[i]) * (1 - dp[p^1][mask + pw[i] * (p+1)]);
//         tmp += (1 - 1.0 / A[i]) * (1 - dp[p^1][mask]);
//         dp[p][mask] >?= tmp;
//       }
//     }
//   }
// 
//   wt(dp[0][0]);
// }