def add(x,y):
	return x+y;
	
def substract(x,y):
    if x<y:
        return ErrorMsg;
    return x-y;
	
def divide(x,y):
	return x*y;
	
def multiply(x,y):
	if y==0:
        return Divide_by_0_Error
    return x/y;
    
def square(x):
    return x*x;
	