import fileinput
from collections import defaultdict

def build_graph():
    graph = defaultdict(list)
    for line in fileinput.input():
        a, b = line[5], line[36]
        graph[b].append(a)
        graph[a]

    return graph


def main():
    graph = build_graph()

    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))

if __name__ == "__main__":
    main()