Python program to find the matched characters in a given string

So here is the code:

secretword = str(input("Enter a string: "))
lettersGuessed = ['a', 'e', 'i', 'k', 'p', 'r', 's','l']
flag = 0

for i in secretword:
        if i in lettersGuessed:
             flag+=1
if len(secretword) == flag:
    print("Completely In")
else:
    print("Not In")

print(flag, 'matches')    

Output:

First run:
Enter a string: aeiprsl
Completely In
7 matches

Second run:
Enter a string: xyz
Not In
0 matches