import fileinput
from collections import defaultdict

def work_seconds(node):
    return ord(node) - ord('A') + 60

graph = defaultdict(set)
for line in fileinput.input():
    a = line[5]
    b = line[36]

    graph[b].add(a)
    graph[a]

order = []
to_consider = sorted(graph.keys())
while to_consider:
    for i, node in enumerate(to_consider):
        parents = graph[node]
        if any(parent in to_consider for parent in parents):
            continue

        order.append(node)
        del to_consider[i]
        break

print("".join(order))