Recently, the answers of a test held nationwide were leaked to a group of unscrupulous people. The investigative agency has arrested the mastermind and nine other people A, B, C, D, E, F, G, H and I in this matter. Interrogating them, the following facts have been obtained regarding their operation. Initially, the mastermind obtains the correct answer-key.
All the others create their answer-key from one or two people who already possess the same. These people are called his/her “sources”. If the person has two sources, then he/she compares
the answer-keys obtained for both sources. If the key to a question from both sources is identical, it is copied, otherwise it is left blank. If the person has only one source, he/she copies the source’s answer into his/her copy. Finally each person compulsorily replaces one of the answers (not a blank one) with a wrong answer in his/her answer key.

The paper contained 200 questions, so the investigative agency has ruled out the possibility of two or more of them introducing wrong answers to the same question. The investigative agency
has a copy of the correct answer key and has tabulated the following data. This data represents question numbers.

Question 170

How many people (excluding the mastermind) needed to make answer keys before C could make his answer key?

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