Работает же...
package com.javarush.task.task08.task0829;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
/*
Модернизация ПО
*/
public class Solution {
public static void main(String[] args) throws IOException {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
List<String> list = new ArrayList<>();
while (true) {
String familyCity = reader.readLine();
String family = reader.readLine();
if (familyCity.isEmpty()) {
break;
}
list.add(familyCity);
list.add(family);
}
// Read the house number
String familyNumber = reader.readLine();
//if (0 <= houseNumber && houseNumber < list.size()) {
// String familyName = list.get(houseNumber);
for (int i=0;i<list.size();i++){
if (list.get(i).equals(familyNumber)) System.out.println(list.get(i+1));
}
/* for (String i: list) {
if (i.equals(familyNumber)) System.out.println(i.next());
}
*/
//System.out.println(familyCity);
}
}