#include <iostream>
#include <cmath>
#include <ctime>
#pragma warning(disable: 4996)
using namespace std;


int main()
{
    long double eps;

    printf("%s","Enter an enpsilon number : ");

    while (true)
    {
        if (scanf_s("%lf", &eps))
        {
            break;
        }
        else
        {
            printf("%s%c", "Retry ",'\n');

        }
    }


    srand(time(0));
    double x;
    x =(((double)rand())/10000)/5-double(1);
    //x = 0.999;
    printf("%s%lf%c", "Generated random x = ", x,'\n');
    long double sum = x, multiplier = 0,current=x;
    int n = 1;
    while (true)
    {
        multiplier = (x*x) * (2*n-1) / (2*n + 1);
        n++;

        if (abs(2*current*(1-multiplier)) <eps)
        {
            break;
        }
        current *= multiplier;
        sum += current;

    }
    sum = 2*sum;
    printf("%s%.16lf%c","Result of program: ", sum,'\n');
    printf("%s%lf%c","Result of standart function: ", log((1+x)/(1-x)),'\n');
}