using System;
using System.Text;
class Program
{
static string convert_part_to_lowercase(string s, int idx) {
int len = s.Length;
if (idx < 0 || idx > len) return s;
StringBuilder sb = new StringBuilder(s);
for (int i = 0; i < len; i++) {
if (i >= idx && (s[i] >= 'A' && s[i] <= 'Z')) {
sb[i] = Char.ToLower(sb[i]);
}
}
return sb.ToString();
}
static void Main() {
string s = "CSHARP PROGRAMMING";
s = convert_part_to_lowercase(s, 4);
Console.Write(s);
}
}
/*
run:
CSHArp programming
*/