import java.util.Scanner;

public class var_27_task_3 {

    public static void main(String[] args){

        Scanner scanner = new Scanner(System.in);

        boolean isIncorrect;
        int precision = 0;

        do {
            System.out.print("Enter precision (number of iterations) : ");
            isIncorrect = false;
            try {
                precision = Integer.parseInt(scanner.nextLine());
            } catch (NumberFormatException exception) {
                isIncorrect = true;

                System.err.println("Input Error. Check if the data is correct.");
            }


            if (!isIncorrect && (precision <= 0)) {
                isIncorrect = true;

                System.err.println("Input Error. Check if the data is correct.");
            }
        } while (isIncorrect);

        scanner.close();

        double pi = 0.0;
        float numerator = 1;
        float firstDenominator = 1;
        float secondDenominator = 3;

        for (int i = 0; i < precision; i++) {
            for(int k = 0; k < 3; k++){
                if (k < 2){
                    pi += numerator/(firstDenominator*secondDenominator);
                } else {
                    pi -= numerator/(firstDenominator*secondDenominator);
                }
                firstDenominator+=4;
                secondDenominator+=4;
            }
        }

        System.out.println("Pi value = " + pi*8);

    }

}