custom robots.txt file in blogger

how to enabled custom robots.txt file in blogger. this is very improtant because crawlers and indexing in google dot com . our blogs index in search engine like google. any people search this our blogs in top of list . and read this custom robots.txt file click the yes then open a blank box copy this paragraph and past it.

User-agent: Mediapartners-Google
Disallow:
User-agent: *
Disallow: /search
Allow: /
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