#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e9 + 7;
const int N = 1e3 + 10;
int main() {
  int t, s, q;
  cin >> t >> s >> q;
  int ans = 0;
  while (s < t) {
    ans++;
    s *= q;
  }
  cout << ans << endl;
  return 0;
}
