stamina breaking when i let go of shift?

when ever i click shift everything goes fine, but when i let go of shift i want the stamina to regen, and i want to be able to run at anytime as long as the stamina is above 0, but when i let go, i cant run anymore, i know i am doing something wrong.

---sprtsp = sprint speed
---regspd = regular speed
---maxstam = max stanima






--- Vars
local plr = game.Players.LocalPlayer
local char = plr.Character
local hum = char.Humanoid
local sprtspd = 30
local regspd = 16
local maxstam = 100
uis = game:GetService("UserInputService")
letgo = false
------------------------------------





uis.InputBegan:connect(function(input)
	
if maxstam > 100 then 
	maxstam = 100
end
	if input.KeyCode == Enum.KeyCode.LeftShift then
			while true do
			hum.WalkSpeed = sprtspd
			maxstam = maxstam - 1 
			wait(0.1)
			print(maxstam)
			if maxstam == 0 then
			hum.WalkSpeed = regspd
			elseif letgo == true then
			hum.WalkSpeed = regspd
			break
			end
		end
	end
end)





uis.InputEnded:connect(function(input)
	

	if input.KeyCode == Enum.KeyCode.LeftShift then
		letgo = true
		while true do
			maxstam  = maxstam + 1
			wait(0.5)
			print(maxstam)
			if maxstam == 100 then
			return
			end
		end
	end
end)

Just a simple problem of not setting the debounce back to false :) (letgo)

---sprtsp = sprint speed
---regspd = regular speed
---maxstam = max stanima
--- Vars
local plr = game.Players.LocalPlayer
local char = plr.Character
local hum = char:WaitForChild("Humanoid")
local sprtspd = 30
local regspd = 16
local maxstam = 100
uis = game:GetService("UserInputService")
letgo = false
------------------------------------
uis.InputBegan:connect(function(input)
	letgo = false -- here
	if maxstam > 100 then 
	    maxstam = 100
	end
    if input.KeyCode == Enum.KeyCode.LeftShift then
		while true do
            hum.WalkSpeed = sprtspd
            maxstam = maxstam - 1 
            wait(0.1)
            print(maxstam)
            if maxstam == 0 then
            	hum.WalkSpeed = regspd
            elseif letgo == true then
            	hum.WalkSpeed = regspd
            	break
            end
        end
    end
end)
uis.InputEnded:connect(function(input)
    if input.KeyCode == Enum.KeyCode.LeftShift then
        letgo = true
        while wait(0.5) do
            maxstam  = maxstam + 1
            print(maxstam)
            if maxstam == 100 then
            return
            end
        end
    end
end)