print((function (fh)
	local n,k,s,t = fh:read("*n"),tonumber(fh:read("*l")),fh:read("*l"),0
	if s:sub(k,k)=="(" then
		for i=k,n do
			t = s:sub(i,i)=="(" and t+1 or t-1
			if t==0 then return i end
		end
	else
		for i=k,1,-1 do
			t = s:sub(i,i)~="(" and t+1 or t-1
			if t==0 then return i end
		end
	end
end)(io.stdin))