#include <bits/stdc++.h>
using namespace std;
const int MAX = 1e5;
int t, s, q;
int main() {
  while (~scanf("%d %d %d", &t, &s, &q)) {
    int ans = 0;
    while (s < t) {
      ans++;
      s *= q;
    }
    printf("%d\n", ans);
  }
  return 0;
}
