import re
s = 'start hamlet of just 50 year-round start residents lacks a grocery store end or even a gasoline station'
print(re.search(r'start((?!.*start.*).*)end', s).group(1))
aW1wb3J0IHJlIAoKcyA9ICdzdGFydCBoYW1sZXQgb2YganVzdCA1MCB5ZWFyLXJvdW5kIHN0YXJ0IHJlc2lkZW50cyBsYWNrcyBhIGdyb2Nlcnkgc3RvcmUgZW5kIG9yIGV2ZW4gYSBnYXNvbGluZSBzdGF0aW9uJwoKcHJpbnQocmUuc2VhcmNoKHInc3RhcnQoKD8hLipzdGFydC4qKS4qKWVuZCcsIHMpLmdyb3VwKDEpKQo=