How to fix the 'variable' was not declared in this scope error?

this code shows error 'len' and 'wid' was not declared in this scope how can I fix it?

class Shape {    
    private:    
        double length;    
        double width;    
    public:  

        Shape(double len, double wid) {  
            length = len;  
            width = wid;  
        }

        double getArea() {   
            return len*wid;    
        }    
};    


int main() {    
    Shape Shape(2,4);    
    cout << Shape.getArea();    
}