#include<bits/stdc++.h>
using namespace std;

using lint = long long;

struct frac {
    lint n,d;
    frac() { n = 0, d = 1; }
    frac(lint _n, lint _d) {
        n = _n, d = _d;
        lint g = __gcd(n,d); n /= g, d /= g;
        if (d < 0) n *= -1, d *= -1;
    }
    frac(lint _n) : frac(_n, 1) {}

    friend frac abs(frac F) { return frac(abs(F.n),F.d); }

    friend bool operator<(const frac& l, const frac& r) { return l.n*r.d < r.n*l.d; }
    friend bool operator==(const frac& l, const frac& r) { return l.n == r.n && l.d == r.d; }
    friend bool operator!=(const frac& l, const frac& r) { return !(l == r); }

    friend frac operator+(const frac& l, const frac& r) { return frac(l.n*r.d+r.n*l.d,l.d*r.d); }
    friend frac operator-(const frac& l, const frac& r) { return frac(l.n*r.d-r.n*l.d,l.d*r.d); }
    friend frac operator*(const frac& l, const frac& r) { return frac(l.n*r.n,l.d*r.d); }
    friend frac operator*(const frac& l, int r) { return l*frac(r,1); }
    friend frac operator*(int r, const frac& l) { return l*r; }
    friend frac operator/(const frac& l, const frac& r) { return l*frac(r.d,r.n); }
    friend frac operator/(const frac& l, const int& r) { return l/frac(r,1); }
    friend frac operator/(const int& l, const frac& r) { return frac(l,1)/r; }

    friend frac& operator+=(frac& l, const frac& r) { return l = l+r; }
    friend frac& operator-=(frac& l, const frac& r) { return l = l-r; }
    template<class T> friend frac& operator*=(frac& l, const T& r) { return l = l*r; }
    template<class T> friend frac& operator/=(frac& l, const T& r) { return l = l/r; }

    friend ostream& operator<<(ostream& strm, const frac& a) {
        strm << a.n;
        if (a.d != 1) strm << "/" << a.d;
        return strm;
    }
};

int main() {
	ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	cout << setprecision(14) << fixed;
	int n;
	cin >> n;
	frac result(0);
	double total = 0.0;
	for (int i = 0; i < n; ++i) {
		lint a;
		cin >> a;
		frac x(1LL, a);
		double k = 1.0/a;
		total = total + k;
		result = result + x;
	}
	double ret = (double)result.d/result.n;
	cout << ret << '\n';
	//cout << (double)1.0/total << '\n'; 
}

