#include <iostream>
#include <string>
#include <algorithm>
 
using namespace std;
 
bool compare(string s1, string s2)
{
	transform(s1.begin(), s1.end(), s1.begin(), ::toupper);
	transform(s2.begin(), s2.end(), s2.begin(), ::toupper);
	return s1 == s2;
}
 
int main() {
 
	string s[] = {"sTAck", "STACk", "STAcK", "SSTTAACCKK", "stack", "Extack"};
 
	for(int i = 0; i < 6; i++)
		cout << s[i] << (compare(s[i], "stack") ? " OK" : " NOK") << endl;
 
	return 0;
}

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