My script will not remove any stamina and I don't know what I have done wrong please help here is the script

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local player = game.Players.LocalPlayer

local UserInp = game:GetService("UserInputService")

local ShiftPressed = false

local stamina = 100

local function ChangeWalkSpeed(Player, NewWalkSpeed) if Player and Player.Character then if Player.Character:FindFirstChildWhichIsA("Humanoid") then Player.Character:FindFirstChildWhichIsA("Humanoid").WalkSpeed = NewWalkSpeed end end end

ChangeWalkSpeed(player, 9)

UserInp.InputBegan:Connect(function(input)

if input.KeyCode == Enum.KeyCode.LeftShift then
	
	if stamina >= 1 then
	
	ShiftPressed = true
	
	while ShiftPressed == true do
		wait()
			ChangeWalkSpeed(player, 36)
			
			end
			
	end

end

end)

UserInp.InputEnded:Connect(function(input)

if input.KeyCode == Enum.KeyCode.LeftShift then
	
	ShiftPressed = false
	
	while ShiftPressed == false do
		wait()
		ChangeWalkSpeed(player, 9)
	end

end

end)

while true do

wait()

if ShiftPressed == true  then

	wait(0.009)
	
	stamina = stamina - 1
	
end

if stamina <= 99 then
	
	print("work")
	
	wait(0.8)
	
	stamina = stamina + 1
	
end

if stamina <= 1 then
	
	wait()
	
	ShiftPressed = false
	
end

print(stamina)

end

Anonymous