/*
 !-----------------------------------------------------
 ! Simulated frequency experiment;
 !
 ! Each switch in the following circuit independently
 ! has probability of 0.5 of being in the "on" state.
 ! The probabilty of points a and b being electrically
 ! connected is then 0.6875.
 !
 !      +--------- s ---------+
 !      |                     |
 !  a---|                     |---b
 !      |         +-- s --+   |
 !      +-- s ----|       |---+
 !                +-- s --+
 !-----------------------------------------------------
*/
#include <iostream>
#include <cstdlib>
#include <iomanip>
using namespace std;

int main() {

  srand ( time(NULL) ); // Randomize the RNG seed.
  int n=100000000;           // n trials
  int h=0;              // Number of successes.

  for (int j=1; j<=n; j++) {

    int s1 = rand() % 2;
    int s2 = rand() % 2;
    int s3 = rand() % 2;
    int s4 = rand() % 2;
    if (  s1  ||  (  s2 && ( s3 || s4 )  )  ) h++;

  }

  cout << fixed << setprecision(9) << setw(12)
       << h/double(n)
       << endl;

}