#include <bits/stdc++.h>
long long int w, m, k;
using namespace std;
int numD(long long n) {
  int num = 0;
  while (n > 0) {
    n = n / 10;
    num++;
  }
  return num;
}
int main() {
  cin >> w >> m >> k;
  long long int cost = 0;
  if (k > w)
    cout << '0' << endl;
  else {
    int dig = numD(m);
    long long count = 0;
    long long int prev = m;
    while (1) {
      long long int next = 1;
      int d = dig;
      while (d--) {
        next *= 10;
      }
      if ((next - prev) < w / (k * dig)) {
        cost += (next - prev) * k * dig;
        dig = dig + 1;
        count += (next - prev);
        prev = next;
      } else {
        if (cost == w) {
          cout << count << endl;
          break;
        } else {
          count += (w - cost) / (dig * k);
          cout << count << endl;
          break;
        }
      }
    }
  }
  return 0;
}
