func main()
	var n: int :: cui@inputInt()
	var k: int :: cui@inputInt()
	do k :- 1
	var a: []int :: #[n]int
	for i(0, n - 1)
		do a[i] :: cui@inputInt()
	end for
	var numL: int :: 0
	var numR: int :: 0
	for i(k - 1, 0, -1)
		do numL :+ a[i]
		if(a[i] <= 1)
			break i
		end if
	end for
	for i(k + 1, n - 1)
		do numR :+ a[i]
		if(a[i] <= 1)
			break i
		end if
	end for
	
	var ans: int :: 0
	switch(a[k])
	case 0
		do ans :: 0
	case 1
		do ans :: 1 + lib@max(numL, numR)
	default
		do ans :: a[k] + numL + numR
	end switch
	
	do cui@print("\{ans}\n")
end func