import sys
n,k,*a=map(int,sys.stdin.read().split())
k-=1
b=bytes(i>1 for i in a)
print(sum((
 sorted([sum(a[b.rfind(0,0,k)-n:k]),sum(a[b.find(0,k+1):k:-1])])+[a[k]]
)[~a[k]:]))