At Pascha you receive 0.5 month pay IF you worked the whole of January, February and March.
In the summer you receive 0.5 month pay IF you worked the whole of April, May and June.
At Christmas you receive 1 month pay IF you worked all July to December.
If you work less than the whole of any one of these periods you should be paid pro-rata. For example work all July, August and September but NOT October, November and December then you should receive 0.5 month at Christmas.