public static int migratoryBirds(List<Integer> arr) {
    // Write your code here
        Map<Integer, Integer> countMap = new HashMap<>();
        
        for (Integer num : arr) {
            if (Objects.isNull(countMap.get(num))) {
                countMap.put(num, 0);
                continue;
            }
            
            int value = countMap.get(num);
            countMap.remove(num);
            countMap.put(num, ++value);
        }
        
        int max = 0;
        int res = 0;
        for (Map.Entry<Integer, Integer> entry : countMap.entrySet()) {
            if (entry.getValue() > max) {
                max = entry.getValue();
                res = entry.getKey();
            }
        }
        
        return res;
    }