# CCC 2020 Problem J2: Epidemiology
# Programmer: Foram Gandhi

def epidemiology():
    p = int(input())
    n = int(input())
    r = int(input())

    infected = n
    people = n

    count = 0
    while True:
        people = people + (infected * r)
        infected = infected * r
        count += 1

        if people >= p:
            if people == p:
                print(count + 1)
            else:
                print(count)
            break
            
epidemiology()
