Problem p03986 (python)

Fixed submission:
x = list(input())
n = len(x)

a = 0
c = 0
for i in range(n):
    if x[n-1-i] == 'S':
        if a >= 1:
            a -=1
            c += 1
    else:
        a += 1

print(n-c*2)

Buggy submission (verdict: Runtime Error):
#root.search(x): ◯.data == x のものが存在するある場合それを出力、ない場合Noneを出力
#root.insert(x): ◯.data == xが存在する場合Falseを出力、ない場合◯.data == x なる頂点を作る
#y.to_s(): 頂点yのdataを出力
#y.left_s(): 頂点yのleftを出力(ない場合はNone)
#root.search_lower(x,None): ○.dataがxより小さいものの中で最も大きいものを出力、ない場合Noneを出力
#root.search_higher(x,None): xより大きいものの中で最も小さいものを出力、ない場合Noneを出力
 
################################################################################
class Avltree:
    def __init__(self,key=None):
        self.key = key
        self.left = None
        self.right = None 
        self.balance = "Even"

    def search_lower(self,key,key_lower):
        if self.key == None:
            return key_lower
        if self.key > key:
            if self.left == None:
                return key_lower
            else:
                return self.left.search_lower(key,key_lower)
        if self.key < key:
            key_lower = self.key
            if self.right == None:
                return key_lower
            else:
                return self.right.search_lower(key,key_lower)
        #self.key == keyの場合
        if self.left == None:
            return key_lower
        else:
            if key_lower == None:
                return self.left.end_higher(self.left.key)
            else:
                return max(key_lower,self.left.end_higher(self.left.key))
    
    def search_higher(self,key,key_higher):
        if self.key == None:
            return key_higher
        if self.key > key:
            key_higher = self.key
            if self.left == None:
                return key_higher
            else:
                return self.left.search_higher(key,key_higher)
        if self.key < key:
            if self.right == None:
                return key_higher
            else:
                return self.right.search_higher(key,key_higher)
        #self.key == keyの場合
        if self.right == None:
            return key_higher
        else:
            if key_higher == None:
                return self.right.end_lower(self.right.key)
            else:
                return min(key_higher,self.right.end_lower(self.right.key))
        
    
    def end_lower(self,end_lower_key):
        if self.left == None:
            return end_lower_key
        else:
            end_lower_key = self.left.key
            return self.left.end_lower(end_lower_key)
    def end_higher(self,end_higher_key):
        if self.right == None:
            return end_higher_key
        else:
            end_higher_key = self.right.key
            return self.right.end_higher(end_higher_key)
    
            
    def DoubleRightRotation(self):
        tl = self.left
        self.left = tl.right.right
        tl.right.right = self # selfはそのノード
        tlr = tl.right
        tl.right = tlr.left
        tlr.left = tl
        if tlr.balance == "Left":
            tlr.right.balance = "Right"
            tlr.left.balance = "Even"
        elif tlr.balance == "Right":
            tlr.right.balance = "Even"
            tlr.left.balance = "Left"
        elif tlr.balance == "Even":
            tlr.right.balance = "Even"
            tlr.left.balance = "Even"
        tlr.balance = "Even"
        return tlr
    def DoubleLeftRotation(self):
        tr = self.right
        self.right = tr.left.left
        tr.left.left = self
        trl = tr.left
        tr.left = trl.right
        trl.right = tr
        if trl.balance == "Right":
            trl.left.balance = "Left"
            trl.right.balance = "Even"
        elif trl.balance == "Left":
            trl.left.balance = "Even"
            trl.right.balance = "Right"
        elif trl.balance == "Even":
            trl.left.balance = "Even"
            trl.right.balance = "Even"
        trl.balance = "Even"
        return trl
    def SingleLeftRotation(self):
        tr = self.right
        tr.balance = "Even"
        self.balance = "Even"
        self.right = tr.left
        tr.left = self
        return tr
    def SingleRightRotation(self):
        tl = self.left
        tl.balance = "Even"
        self.balance = "Even"
        self.left = tl.right
        tl.right = self
        return tl
    def replace(self,p,v): # 親ノードpの下にある自分(self)をvに置き換える。
        if p.left == self:
            p.left = v
        else :
            p.right = v 
    def insert(self,key): # rootでのみ呼ばれる挿入
        if self.key == None: # rootを含むrotationはしないことにする。
            self.key = key
            return self
        if key < self.key:
            if self.left == None:
                self.left = Avltree(key)
            else:
                self.left.insertx(self,key)
        elif key > self.key:
            if self.right == None:
                self.right = Avltree(key)
            else:
                self.right.insertx(self,key)
        else: # key == self.key:
            pass # do not overwrite
    def insertx(self,p,key): # replaceを呼ぶために一つ上の親を持っているinsert
        if self.key > key:
            if self.left == None:
                self.left = Avltree(key)
            else:
                if not self.left.insertx(self, key): # 左の木が生長しなければ、
                    return False # 成長しない
            if self.balance == "Right":
                self.balance = "Even"
                return False
            elif self.balance == "Even":
                self.balance = "Left"
                return True # 成長した
            elif self.balance == "Left":
                if self.left.balance == "Right":
                    self.replace(p,self.DoubleRightRotation())
                elif self.left.balance == "Left":
                    self.replace(p,self.SingleRightRotation())
                return False # rotationを行うと成長しない
        if self.key < key:
            if self.right == None:
                self.right = Avltree(key)
            else:
                if not self.right.insertx(self, key):
                    return False 
            if self.balance == "Left":
                self.balance = "Even"
                return False
            elif self.balance == "Even":
                self.balance = "Right"
                return True
            elif self.balance == "Right":
                if self.right.balance == "Left": 
                    self.replace(p,self.DoubleLeftRotation())
                elif self.right.balance == "Right":
                    self.replace(p,self.SingleLeftRotation())
                return False
        return False # self.key == keyの時は何もしないので成長もしない 


################################################################

def inpl(): return [int(i) for i in input().split()]
n = int(input())
a = inpl()
b = {a[i]: i for i in range(n)}

root = Avltree()
ass = 0

for i in range(1,n+1):
    l = root.search_lower(b[i],None)
    r = root.search_higher(b[i],None)
    if l == None:
        l = -1
    if r == None:
        r = n
    ass += (b[i]-l)*(r-b[i])*i
    root.insert(b[i])
print(0)