interface Refer
{ String m(String s); }

class StringOperation
{
	String reverse(String s)
	{   String res = "";
		for(int i=s.length()-1; i>=0; i--)
			res += s.charAt(i);
		return res;
	}
}

public class ReferDemo
{ 	
    static String compute(Refer r, String s)
	{ return r.m(s); }
	
    public static void main(String[] args)
	{   String s = "sample string";
		System.out.println(compute(new StringOperation()::reverse, s));
		/*
		Refer ob = (str)->{
			String res = "";
		for(int i=s.length()-1; i>=0; i--)
			res += s.charAt(i);
		return res;
		};
		
		System.out.println(compute(ob, s));
		*/
	}
}