#include <random>
#include <iostream>

std::random_device rd;
std::uniform_int_distribution<int> distribution(0, 1);
std::mt19937 engine(rd()); // Mersenne twister MT19937

bool coin ()
{
    return distribution (engine);
}

int main ()
{
    int a = 1000;
    int b = 0;

    for (int i = 0; i < a; ++i)
        b += (coin () ? 1 : 0);

    std :: cout << "Verify coin(): " << b << "/" << a << "\n\n";

    for (long int TRIALS = 10; TRIALS < 1000000000000; TRIALS *= 10)
    {
        long double winnings = 0;

        for (int i = 0; i < TRIALS; ++i)
        {
            long double pot = 2;

            if (! coin ())
                continue;

            while (true)
            {
                if (! coin ())
                    break;

                pot *= 2;
            }

            // std :: cout << "Won $" << pot << "\n";

            winnings += pot;
        }

        std :: cout << TRIALS << ",\t" << (winnings / TRIALS) << "\n"
            << std :: flush;
    }
}