求大神解答，为啥报错

Question

import java.util.Scanner;

public class Rectangle extends Shape {

@Override

public void zhouchang() {

// TODO Auto-generated method stub

System.out.println("请输入长方形的长度：");

int a=input.nextInt();

System.out.println("请输入长方形的宽度：");

int b=input.nextInt();

int num=a+b;

System.out.println("长方形的周长为"+num);

}

报错

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 

input cannot be resolved

为啥啊？是因为不是main方法？