I wanted to make the legs longer, so I

• cast-on 108 st
• worked chart
• added 1 purl round
• worked 31 rounds in stockinette increasing 1 st at beginning of the round and 1 st at the middle on rounds n° 4 - 8 - 12 - 16 - 20 - 24 & 28 ➔ 122 st
• worked crotch and decreases as per pattern
• then, when about to knit the 15 last rounds before waistband :

. K 1 round
. K39 turn
. Make Double Stitch P6 Turn
. Make Double Stitch K1 Central Double Decrease K5 Turn
. Make Double Stitch P10 Turn
. Make Double Stitch K13 Turn
. Make Double Stitch P16 Turn
. Make Double Stitch K19 Turn
. Make Double Stitch P22 Turn
. Make Double Stitch K25 Turn
. Make Double Stitch P28 Turn
. Make Double Stitch K31 Turn
. Make Double Stitch P34 Turn
. Make Double Stitch K37 Turn
. Make Double Stitch P40 Turn
. Make Double Stitch K43 Turn
. Make Double Stitch P46 Turn
. Make Double Stitch K49 Turn
. Make Double Stitch P52 Turn
. Make Double Stitch K55 Turn
. Make Double Stitch P58 Turn
. Make Double Stitch K61 Turn
. Make Double Stitch P64 Turn
. Make Double Stitch K137
. K 23 rounds (but that’s too much 13 would have been enough)

• finish waistband as per pattern