Olivier, don't go by the metric measurement. Count the number of points horizontally and vertically. I count 14 across, and 17-18 vertically, with a row of half-size points at the top. By my count this is an E-grill, Scott number 89.
This cats at $350 in sound VF grade, but your stamp is off in two directions and has trimmed perfs on at least three sides, and has a bit of wrinkling at the top. I assume the red spot to be from a transit mark, but if it is a stain, that hurts some more. I did not check, but I suspect that this stamp would sell on
ebay in the range of $20-35 US. Others can give you a better estimate of value.