How to delete certain lines of text in Notepad using regular expressions?

Question

Regular Expressions

There is a file in txt format
A line with some letters, numbers and symbols
1 A line with some letters, numbers and symbols
2 A line with some letters, numbers and symbols
3 A line with some letters, numbers and symbols 4 A
line with some then letters, numbers and symbols5 A
string with some letters, numbers and symbols6
A string with some letters, numbers and symbols7 A string with some letters, numbers and symbols

Answer 1

https://regex101.com/r/71hybK/1
Find: (?m-s)^(.+)(\n.+){2}
Replace:$1