if on simple test your answer is
141.82419374396696000000
373.90014714318562000000
528.61744940933136000000
605.97610054240431000000
605.97610054240431000000
528.61744940933136000000
373.90014714318562000000
141.82419374396696000000

just swap(a,b) and read carefully problem; =)