#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


using Double = long double;
constexpr Double INF = 1e+100;

// max (p x + q),  p: incr.
struct ConvexMax {
  vector<pair<Double, Double>> lines;
  vector<Double> xs;
  ConvexMax() : lines{}, xs{} {}
  friend ostream &operator<<(ostream &os, const ConvexMax &f) {
    return os << "(" << f.lines << ", " << f.xs << ")";
  }
  void add(Double p, Double q) {
    if (lines.size() >= 1 && lines.back().first == p && lines.back().second >= q) return;
    for (; lines.size() >= 1; lines.pop_back(), xs.pop_back()) {
      assert(lines.back().first <= p);
      if (lines.back().first == p) continue;
      const Double x = (q - lines.back().second) / (lines.back().first - p);
      if (xs.back() < x) {
        lines.emplace_back(p, q);
        xs.push_back(x);
        return;
      }
    }
    lines.emplace_back(p, q);
    xs.emplace_back(-INF);
  }
  void add(const pair<Double, Double> &line) {
    add(line.first, line.second);
  }
  Double operator()(Double x) const {
    if (!lines.size()) return -INF;
    const int pos = upper_bound(xs.begin(), xs.end(), x) - xs.begin() - 1;
    return lines[pos].first * x + lines[pos].second;
  }
};

////////////////////////////////////////////////////////////////////////////////


int N;
vector<Double> P;

int main() {
  for (; ~scanf("%d", &N); ) {
    P.resize(N + 1);
    for (int i = 1; i <= N; ++i) {
      scanf("%Lf", &P[i]);
    }
    P[0] = 1;
    
    vector<Double> dp(N + 1);
    ConvexMax con;
    for (int i = N; i >= 0; --i) {
      dp[i] = max<Double>(i, con(-i));
      con.add(-(1 - P[i]), P[i] * dp[i]);
    }
    printf("%.20Lf\n", dp[0]);
  }
  return 0;
}