One day, Ks raised a question in this contest. How many times the digit 7texttt{7}7 appears in the integer range of [0, n]?
One day, Ks raised a question in this contest. How many times the digit 7texttt{7}7 appears in the integer range of [0, n]? The answer may be very large, please output the answer modulo 1 000 000 0071,000,000,0071000000007.
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标签： HBC206672777题解
