#include <bits/stdc++.h>

using namespace std;

int fact(int n)
{
    if(n == 1 || n == 0)
        return 1;
    
    return n * fact(n-1);
}

/*             /n\
   b(x,n,p) = |   | * p^x * q^(n-x)
               \x/
*/
double binominal_probability(int x, int n, double p)
{
    int    a = fact(n)/(fact(x)*fact(n-x));
    double b = pow(p,x);
    double c = pow(1-p,n-x);
    return a*b*c;
}

int main() {
    // Number of trials
    int n = 6;
    
    // Ratio of boys being born
    double rboy = 1.09;

    // Ratio of girls being born
    double rgirl = 1;

    // Probability of giving birth to a boy
    double p = rboy/(rboy+rgirl);

    //what proportion of Russian families with exactly 6 children will
    // have at least 3 boys?
    
    // p(x >= 3)
    cout << fixed << setprecision(3) <<
        binominal_probability(3,n,p)
        + binominal_probability(4,n,p)
        + binominal_probability(5,n,p)
        + binominal_probability(6,n,p) << endl;
    return 0;
}