#include <bits/stdc++.h>
using namespace std;
inline int dig_count(long long n) {
  int count = 0;
  while (n) {
    n = n / 10;
    count++;
  }
  return count;
}
inline long long next_dig_num(int n) {
  long long res = 1;
  for (int i = 0; i < n - 1; i++) {
    res = res * 10;
  }
  return res;
}
int main() {
  long long sum = 0, next, final, left_num, afford_num, m, k, w, i, j;
  int dig;
  cin >> w >> m >> k;
  dig = dig_count(m);
  next = next_dig_num(dig + 1);
  do {
    left_num = next - m;
    afford_num = w / (dig * k);
    final = min(afford_num, left_num);
    sum += final;
    m = next;
    next = next * 10;
    w = w - (final * k * dig);
    dig++;
  } while (final != 0 && w > 0);
  cout << sum << endl;
}
