
76  ZOJ 7th Anniversary Contest  A
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 Kth digit of M^n is 7, what is the smallest n? Input Each case is given in a line with 2 numbers: K and M (< 1,000). Output For each test case, please output in a line the smallest n. You can assume:
Sample Input 3 2 4 2 4 3 Sample Output 15 21 11 Author: CHEN, Yue Source: ZOJ 7th Anniversary Contest 