#include <bits/stdc++.h>
using namespace std;
void task() {
  int s, t, q, r = 1;
  long long tm, cs;
  cin >> t >> s >> q;
  cs = s;
  while (cs < t) {
    tm = cs;
    cs = (q - 1) * tm + cs;
    if (cs < t) r++;
  }
  cout << r;
}
int main() {
  ios_base::sync_with_stdio(false);
  task();
  return 0;
}
