37. In the hundred-digit number $12345678901234567890 \ldots 1234567890$, all digits in odd positions were erased. In the resulting fifty-digit number, digits in odd positions were erased again. The erasing continued until nothing was left. What was the last digit to be erased?
37. The first time, 50 odd digits were crossed out, leaving 50 even ones. The second time, 25 digits were crossed out, including 5 twos, 5 fours, 5 sixes, 5 eights, and 5 zeros. 25 remained in the following sequence: $4,8,2,6,0,4$, $8,2,6,0, \ldots, 2,6,0$. (The group of digits 4, 8, 2, 6,0 is written in sequence 5 times.) During the third crossing out, 13 digits will be crossed out, leaving 12 such digits: $8,6,4,2,0,8,6,4,2,0,8,6$. After the fourth crossing out, $6,2,8,4$, 0,6 will remain, after the fifth $-2,4,6$ and after the sixth - 4. Therefore, the last (seventh) time, the digit 4 will be crossed out.