#include <iostream>
using namespace std;
string char_to_lowercase(string s, int idx) {
if (idx < 0 || idx > s.length()) return s;
for (int i = 0; i < s.length(); i++) {
if (i >= idx) {
s[i] = tolower(s[i]);
}
}
return s;
}
int main() {
string s = "CPP PROGRAMMING";
s = char_to_lowercase(s, 6);
cout << s;
}
/*
run:
CPP PRogramming
*/