t,s,q=map(int,input().split())
p=0
while s<t:s=s*q;p+=1
print(p)
1679B - Stone Age Problem | 402A - Nuts |
792A - New Bus Route | 221A - Little Elephant and Function |
492C - Vanya and Exams | 1369B - AccurateLee |
892B - Wrath | 999A - Mishka and Contest |
727C - Guess the Array | 1625C - Road Optimization |
1715D - 2+ doors | 267A - Subtractions |
1582A - Luntik and Concerts | 560A - Currency System in Geraldion |
946A - Partition | 1068B - LCM |
1692E - Binary Deque | 679A - Bear and Prime 100 |
488A - Giga Tower | 14A - Letter |
1150A - Stock Arbitraging | 1552A - Subsequence Permutation |
1131F - Asya And Kittens | 1475F - Unusual Matrix |
133B - Unary | 1547A - Shortest Path with Obstacle |
624A - Save Luke | 1238A - Prime Subtraction |
1107C - Brutality | 1391B - Fix You |