package com.itranswarp.learnjava;

/**
 * for练习
 * 
 */
public class Main {

	public static void main(String[] args) {
		double pi = 0;
		int m = 1;
		for (int i = 1; i<10000; i += 2) {
			pi=pi+1.0/i*m;//m实现正负号的变换。
			m=(-1)*m;
			
		}
		System.out.println(4*pi);
	}

}