7H-​Pyrido[1,​2,​3-​de]​-​1,​4-​benzoxazine-​6-​carboxylic acid, 9-​fluoro-​2,​3-​dihydro-​3-​methyl-​10-​(4-​methyl-​1-​piperazinyl)​-​7-​oxo-​, hydrochloride (1:?)