Space Invaders

Peterwrote hisversion of thepopular game"Space Invaders".The gameis as follows.Onthe groundattackships ofSpace Invaders.Theylined upin rowsat the topof the screen.The player controls alaser gun, which is locatedat the bottom ofthe screenin one of thecolumns.Forone actiona player canmove thegunleft or right, ormake a shotstraight up.If a playermakesa shot, itdestroys thealien shipcomingin thatcolumn,in which thegun.

Unlike the originalgame,Petyaembodiment ofalien shipsarein place andcan not shoot, so theplayer can notlose.Help thePetedestroy allalien shipsin a minimumnumber of operations.

Input

The firstline containsthe numbern and p - number of columns andcolumn number, whichis initiallya gun (1 ≤ n ≤ 100, 1 ≤ p ≤ n). The second linecontainsn numbersa₁, a₂, ..., a_n, where a_i - the number ofaliensin the i^th column (1 ≤ a_i ≤ 100).

Output

In theoutput fileoutputa single number -the minimum number ofoperationsrequiredtodestroy all thealiens.