#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
using ll = long long;
using P = pair<int,int>;

const int n = 20;
const int n2 = 1<<n;
const vector<int> p = {2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71};
 

int main() {
  ll a, b;
  cin >> a >> b;
  vector<ll> dp(n2);
  dp[0] = 1;
  for (ll x = a; x <= b; x++) {
    int s = 0;
    rep(i, n) if(x % p[i] == 0) s |= 1 << i;
    rep(i, n2) {
      if (i & s) continue;
      dp[i|s] += dp[i];
    }
  }

  ll ans = 0;
  rep(i, n2) ans += dp[i];
  cout << ans << endl;

  return 0;
}
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,avx512f")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <iostream>
#include <iomanip>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <list>
#include <stack>
#include <queue>
#include <bitset>
#include <numeric>
#include <cassert>
#include <memory>
#include <random>
#include <functional>
#include <complex>
#include <immintrin.h>
#ifdef DEBUG
#include "./CompetitiveProgrammingCpp/debug_VC.hpp"
#include "./CompetitiveProgrammingCpp/Timer.hpp"
#include "./CompetitiveProgrammingCpp/sample.hpp"
#else
#define dump(...)
#endif

/* macro */
#define FOR(i, b, e) for(ll i = (ll)(b); i < (ll)(e); ++i)
#define RFOR(i, b, e) for(ll i = (ll)(e-1); i >= (ll)(b); --i)
#define REP(i, n) FOR(i, 0, n)
#define RREP(i, n) RFOR(i, 0, n)
#define REPC(x,c) for(const auto& x:(c))
#define REPI2(it,b,e) for(auto it = (b); it != (e); ++it)
#define REPI(it,c) REPI2(it, (c).begin(), (c).end())
#define RREPI(it,c) REPI2(it, (c).rbegin(), (c).rend())
#define REPI_ERACE2(it, b, e) for(auto it = (b); it != (e);)
#define REPI_ERACE(it, c) REPI_ERACE2(it, (c).begin(), (c).end())
#define ALL(x) (x).begin(),(x).end()
#define cauto const auto&
/* macro func */
template<class T>
inline auto sort(T& t) { std::sort(ALL(t)); }
template<class T>
inline auto rsort(T& t) { std::sort((t).rbegin(), (t).rend()); }
template<class T>
inline auto unique(T& t) { (t).erase(unique((t).begin(), (t).end()), (t).end()); }
template<class T, class S>
inline auto chmax(T& t, const S& s) { if (s > t) { t = s; return true; } return false; }
template<class T, class S>
inline auto chmin(T& t, const S& s) { if (s < t) { t = s; return true; } return false; }
inline auto BR() { std::cout << "\n"; }

/* type define */
using ll = long long;
using PAIR = std::pair<ll, ll>;
using VS = std::vector<std::string>;
using VL = std::vector<long long>;
using VVL = std::vector<VL>;
using VVVL = std::vector<VVL>;
using VD = std::vector<double>;
template<class T>
using V = std::vector<T>;

/* using std */
using std::cout;
constexpr char endl = '\n';
using std::cin;
using std::pair;
using std::string;
using std::stack;
using std::queue;
using std::vector;
using std::list;
using std::map;
using std::unordered_map;
using std::multimap;
using std::unordered_multimap;
using std::set;
using std::unordered_set;
using std::unordered_multiset;
using std::multiset;
using std::bitset;
using std::priority_queue;

/* Initial processing  */
struct Preprocessing { Preprocessing() { std::cin.tie(0); std::ios::sync_with_stdio(0); }; }_Preprocessing;

/* Remove the source of the bug */
signed pow(signed, signed) { assert(false); return -1; }

/* define hash */
namespace std {
template <>	class hash<std::pair<ll, ll>> { public:	size_t operator()(const std::pair<ll, ll>& x) const { return hash<ll>()(1000000000 * x.first + x.second); } };
}

/* input */
template<class T> std::istream& operator >> (std::istream& is, vector<T>& vec) { for (T& x : vec) is >> x; return is; }

/* constant value */
constexpr ll MOD = 1000000007;
//constexpr ll MOD = 998244353;

//=============================================================================================


signed main() {
	ll n;
	cin >> n;
	VD v(n);
	cin >> v;

	auto val = [&](double d) {
		double ans = 0.0;
		REPC(x, v) {
			ans += (d + x) / n;
			ans -= std::min(x, 2.0 * d) / n;
		}
		return ans;
	};

	double low = 0;
	double high = 1e15;
	int cnt = 500;
	while (cnt--) {
		double c1 = (low * 2 + high) / 3;
		double c2 = (low + high * 2) / 3;

		if (val(c1) > val(c2)) low = c1;
		else high = c2;
	}
	cout << std::fixed << std::setprecision(15)
		<< val(low) << endl;
}


