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ZOJ Problem Set - 3167
Find 7 Faster Than John Von Neumann

Time Limit: 1 Second      Memory Limit: 32768 KB

It was said that when testing the first computer designed by von Neumann, people gave the following problem to both the legendary professor and the new computer: If the 4th digit of 2^n is 7, what is the smallest n? The machine and von Neumann began computing at the same moment, and von Neumann gave the answer first.

Now you are challenged with a similar but more complicated problem: If the K-th digit of M^n is 7, what is the smallest n?


Each case is given in a line with 2 numbers: K and M (< 1,000).


For each test case, please output in a line the smallest n.

You can assume:

  1. The answer always exist.
  2. The answer is no more than 100.

Sample Input

3 2
4 2
4 3

Sample Output


Author: CHEN, Yue
Source: ZOJ 7th Anniversary Contest
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