题解 | #计算日期到天数转换#

import java.util.Scanner;

public class Main { public static void main(String[] srgs) {

    Scanner scanner = new Scanner(System.in);
    int num = scanner.nextInt(); 
    int sum = 2 * num + 3 * ((num-1 ) * num / 2);
    System.out.print(sum);
}

}