#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  long double t, s, q;
  cin >> t >> s >> q;
  int ans = 1;
  while (s * pow(q, ans) < t) {
    ans++;
  }
  cout << ans;
  return 0;
}
