#include <bits/stdc++.h>
#pragma GCC optimize("O3")
using namespace std;
long long w, m, k;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
  cin >> w >> m >> k;
  long long aa = 0;
  int nc = 0;
  while (aa < m) aa = aa * 10 + 9, ++nc;
  long long m2 = m;
  while (w) {
    if ((aa - m + 1) <= w / k / nc) {
      w = w - k * (aa - m + 1) * nc;
      ++nc;
      m = aa + 1;
      aa = aa * 10 + 9;
    } else {
      m = m + w / k / nc;
      break;
    }
  }
  cout << m - m2;
  return 0;
}
