#include <bits/stdc++.h>
using namespace std;
const double EPS = 1e-7;
const double PI = acos(-1.0);
const double ZERO = 0;
const double DOUBLE_MAX = 1 / ZERO;
int main() {
  long double t, s, q;
  cin >> t >> s >> q;
  long double speed = (q - 1) / q;
  long double x = 0, d;
  int res = 0;
  while (t - s > 1e-9) {
    x += s * speed;
    while (t - s > 1e-9 && x > 1e-10) {
      s += (x) + 1e-9;
      x *= speed;
    }
    res++;
  }
  cout << res;
}
