Materials
11 (12, 13, 14, 15) x 50 g balls in main colour and,
1 ball in contrast colour.

From the pattern description:

Easy to knit in stocking stitch with virtually no shaping, except for the sleeves. Even the collar is knitted as part of the back and fronts.

Erratum
The shaping for the shoulders on the back piece: cast off the number of stitches (as given) on both sides to form a collar. The English pattern only has cast off for one row/side.