using System;
using System.Text.RegularExpressions;
class Program
{
static String extract_characters(String s) {
int len = s.Length;
var regx = new Regex("[a-zA-Z]");
String chars = "";
for (int i = 0; i < len; i++) {
char ch = s[i];
if (regx.IsMatch(ch.ToString()))
chars = chars + ch;
}
return chars;
}
static void Main() {
String s = "c++$vb.NET&%java*() php c# <>/python 3.7.3";
Console.WriteLine(extract_characters(s));
}
}
/*
run:
cvbNETjavaphpcpython
*/