interface Circle {
  kind: "circle";
  radius: number;
}

interface Square {
  kind: "square";
  side: number;
}

type Shape = Circle | Square;

export function getArea(shape: Shape): number {
  if(shape.kind === 'circle'){
    return Math.PI * shape.radius * shape.radius
  } 
  return shape.side * shape.side;
}