#include <bits/stdc++.h>
using namespace std;
int main() {
  int S, S_dif, v, num = 1;
  cin >> S >> S_dif >> v;
  while (S_dif * v < S) {
    num = num + 1;
    S_dif = S_dif * v;
  }
  cout << num;
  return 0;
}
