#!/usr/local/bin/python3

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

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

for _ in range(len(bb)):
    for i, pair in enumerate(bb):
        if cur in pair: break
        raise
    cur = pair[1] if pair[0] == cur else pair[0]
    ans.append(cur)
    del bb[i]

print(ans)