#include <bits/stdc++.h>
using namespace std;
long long w, m, k, n, q, r, res, p, up;
int S(long long n) {
  int cnt = 0;
  while (n) {
    cnt++;
    n /= 10;
  }
  return cnt;
}
int main() {
  cin >> w >> m >> k;
  n = S(m);
  p = pow(10.0, (double)n);
  up = p - m;
  q = w / (k * n);
  if (q <= up)
    res = q;
  else
    res = up;
  w -= res * n * k;
  while (q > up) {
    n++;
    up = pow(10.0, (double)n) - pow(10.0, (double)(n - 1));
    q = w / (k * n);
    if (q <= up) {
      res += q;
      w -= q * n * k;
    } else {
      res += up;
      w -= up * n * k;
    }
  }
  cout << res << endl;
}
