from collections import deque

def search(airport, tickets):
    queue = deque()

    visited = []
    max_visited = []
    used = []
    
    queue.append((airport, visited, used))
    while queue:
        current = queue.popleft()
        airport = current[0]
        visited = current[1]
        used = current[2]
        
        for index, ticket in enumerate(tickets):
            if str(index) not in used and ticket[0] == airport:
                queue.append((ticket[1],visited + [airport], used + [str(index)]))

        if len(max_visited) < len(visited + [airport]):
            max_visited = visited + [airport]
            
    return max_visited


def solution(tickets):

    tickets = sorted(tickets)
    airport = "ICN"

    answer = search(airport, tickets)
    return answer