
ZOJ Problem Set  3167
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 