#include <bits/stdc++.h>

using namespace std;

// The probability that a machine produces a defective product is
// 1/3. What is the probability that the 1st defect is found during
// the first 5 inspections?

int main() {
    double p = 1.0/3.0;
    
    auto geometric_dist = [](int n, double p)
    {
        // The geometric distribution is a special case of the negative
        // binomial distribution that deals with the number of Bernoulli
        // trials required to get a success (i.e., counting the number of
        // failures before the first success).
        
        // g(n,p) = q^(n-1) x p
        
        return pow(1-p, n-1) * p;
    };
    
    double out = 0;
    // sum the probability of defect for each inspection
    for (auto n: {1,2,3,4,5})
        out += geometric_dist(n, p);
                
    cout << fixed << setprecision(3) << out << endl;
    
    return 0;
}