class AproxPI{
	public static void main (String[] args){
		AproxPI p = new AproxPI();
		System.out.println(p.aprox_pi(5));
	}

	public double aprox_pi(int term){
		double pi = 1.0;
		double denominator = 3.0;
		boolean is_addition = false;
		int i;
		for(i=0; i<=term; i++){
			if(is_addition){
				pi = pi + (1.0/denominator);
				is_addition = false;
			}
			else{
				pi = pi - (1.0/denominator);
				is_addition = true;
			}
			denominator = denominator + 2.0;
		}
		return (4*pi);
	}
}