# Define a function calculate_val() that has two parameters and returns the result of subtracting the product of 2 
# And the second parameter from the first parameter 

def calculate_val(x,y): 
    result = x - (2 *y)
    return result 

value_read1 = float(input())
value_read2 = float(input())

print(f' {calculate_val(value_read1, value_read2):.2f}')