#include <bits/stdc++.h>
using namespace std;
const int N = 10e5;
int arr[N];
int main() {
  int t, s, q;
  cin >> t >> s >> q;
  int n = 0;
  while (s < t) {
    s *= q;
    n += 1;
  }
  cout << n;
  return 0;
}
