struct Rectangle {
    width: i32,
    height: i32,
}

impl Rectangle {
    fn new(width: i32, height: i32) -> Rectangle {
         Rectangle { width, height}
    }

    fn area(&self) -> i32 {
        self.width * self.height
    }
}

fn main() {
    let rect = Rectangle::new(30, 50);

    println!("The area of rectangle is {}.", rect.area());
}