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diff --git a/‎src/test/java/com/macasaet/Day25.java
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+package com.macasaet;
+
+import java.io.IOException;
+import java.util.stream.Collectors;
+import java.util.stream.StreamSupport;
+
+public class Day25 {
+
+    public static void main(final String[] args) throws IOException {
+        try (var spliterator = new LineSpliterator(Day22.class.getResourceAsStream("/day-25-input.txt"))) {
+            final var publicKeys = StreamSupport.stream(spliterator, false)
+                    .map(Integer::parseInt)
+                    .collect(Collectors.toUnmodifiableList());
+            final int cardPublicKey = publicKeys.get(0);
+            final int doorPublicKey = publicKeys.get(1);
+            final long initialSubjectNumber = 7;
+
+            int cardLoopSize = 0;
+            for (long value = 1; value != cardPublicKey; cardLoopSize++) {
+                value = transformOnce(value, initialSubjectNumber);
+            }
+            System.out.println("cardLoopSize: " + cardLoopSize);
+
+            int doorLoopSize = 0;
+            for (long value = 1; value != doorPublicKey; doorLoopSize++) {
+                value = transformOnce(value, initialSubjectNumber);
+            }
+            System.out.println("doorLoopSize: " + doorLoopSize);
+
+            final long e1 = transformCompletely(doorPublicKey, cardLoopSize);
+            final long e2 = transformCompletely(cardPublicKey, doorLoopSize);
+            System.out.println("e1: " + e1);
+            System.out.println("e2: " + e2);
+        }
+    }
+
+    protected static long transformCompletely(final long subjectNumber, final int loopSize) {
+        long value = 1;
+        for (int i = loopSize; --i >= 0; value = transformOnce(value, subjectNumber)) ;
+        return value;
+    }
+
+    protected static long transformOnce(final long value, final long subjectNumber) {
+        return (value * subjectNumber) % 20201227;
+    }
+
+}