Pencil and paper. That is the answer. Never mind this new-fangled electronic stuff. That might give you the answer very fast, but only pencil and paper will give you the algorithm. That's what I keep telling our undergraduates, and a few eventually get the message. You also need an eraser. That is far and away the most important piece of hardware required. So get a large one.
Joking aside, you need to write down very simply on a sheet of paper how you are going to get the answer (by the way, 1m 34cm 6mm is a very unusual way to express a length). When I say simply I mean simply: get it down to words of one syllable. Now you have pseudo-code, which enables you to work out the real code easily.
53in = 1346.2mm, so how are you getting 1346? Your arithmetic appears correct, but how are you converting it to a whole number?
Remind yourself of the
five arithmetic operators available in all the C-based languages (Java included).