题解 | 等差数列

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static int getNum(int a1,int d,int n){
        int sum=0;
        sum=a1+(n-1)*d;
        return sum;
    }
    public static int getSum(int a1,int d,int n){
        int result=0;
        int an=getNum(a1,d,n);
        if(n==1){
            result=a1;
        }else if(a1==an){
            result= a1*n;
        }else{
            result=(a1+an)*n/2;
        }
        
        return result;
    }
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNext()) { // 注意 while 处理多个 case
            int n = in.nextInt();
            int result = getSum(2,3,n);
            System.out.println(result);
        }
    }
}