Help in solving snakproc problem

help
,
1

My issue

My code

# cook your dish here
for _ in range(int(input())):
    Length=int(input())
    s=input()
    flag=False
    s=''.join(i for i in s if i!='.')
    for i in range(len(s)-1):
        if s[0]=='T':
            flag=True
            break 
        elif s[i]==s[i+1]:
            flag=True 
            break 
        elif s[len(s)-1]=='H':
            flag=True 
            break 
    if flag==False:
        print("Valid")
    else:
        print("Invalid")

Problem Link: SNAKPROC Problem - CodeChef