#!/usr/local/bin/python3

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

ans = []
cur = sta
ans.append(cur)
bb = b.copy()

while bb:
    for i, pair in enumerate(bb):
        if cur not in pair: continue
        cur = pair[1] if pair[0] == cur else pair[0]
        ans.append(cur)
        del bb[i]
        break
    raise Exception('次にバトンを渡す{}が見付かりません'.format(cur))

print(ans)