Sounds like you're starting with 50 sts: 18 per shoulder (2x18=36) plus 14 for the neck. Work 18, then BO the center 14 for the neck (you'll need to work 2 sts of the 14 and then start the BOs so you don't mistakenly BO sts from the shoulder). BO until there are 18 sts remaining and work to end of row. On the next row, work to w/in a few sts of the neck BOs, and do a dec. You'll need to attach new yarn to the other shoulder. Work the matching dec as you begin that shoulder (same row). Work to end. Turn and continue working both sides at the same time, with their respective balls of yarn, til they measure 56 cm.
Keeping to the knitting basics