#!/usr/local/bin/python3

start = 'yamada'
b = [('suzuki', 'satou'), ('yamada', 'tanaka'), ('tanaka', 'satou'), ('watanabe', 'suzuki')]

ans = []
baton_holder = start
ans.append(baton_holder)
pairs = b.copy()

while pairs:
    found = False
    for i, pair in enumerate(pairs):
        if baton_holder not in pair:
            continue
        found = True
        baton_holder = pair[(pair.index(baton_holder)+1)%2]
        ans.append(baton_holder)
        del pairs[i]
        break
    if not found:
        raise Exception('{} is not found'.format(baton_holder))

print(ans)