#include <bits/stdc++.h>
using namespace std;
long long w, m, k, ans, digit, ori;
void get_ans(long long lft, long long digit) {
  long long res = 1;
  for (int(i) = 0; (i) < digit - 1; i++) res *= 10;
  lft /= k * digit;
  if (ori == digit)
    cout << lft;
  else
    cout << res + lft - m;
  exit(0);
}
int main() {
  cin >> w >> m >> k;
  long long mm = m;
  while (mm) digit++, mm /= 10;
  ori = digit;
  long long mx = 1;
  for (int(i) = 1; (i) <= digit; i++) mx *= 10;
  if (w / (mx - m) / k / digit <= 0)
    get_ans(w, digit);
  else {
    long long cost = (mx - m) * k * digit;
    w -= cost;
  }
  while (true) {
    digit++;
    long long old_mx = mx;
    mx *= 10;
    if (w / (mx - old_mx) / k / digit <= 0)
      get_ans(w, digit);
    else {
      long long cur_cost = (mx - old_mx) * k * digit;
      w -= cur_cost;
    }
  }
  return 0;
}
