package cn.edu.bjut.chapter2;

public class TwoPowerSummation {
	public static void main(String[] args) {
		int sum = 0; 
		for (int n = 1; n <= 20; n++) {
			sum += (int) Math.pow(2, n) - 1; 
		}
		
		System.out.println(sum);
	}
}