#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
const int SIZE = 1e6 + 10;
const long long INF = 1e18;
long long up[18];
int main() {
  up[0] = 1;
  up[1] = 10;
  for (int i = (2); i < (18); ++i) up[i] = up[i - 1] * 10;
  long long w, m, k;
  cin >> w >> m >> k;
  long long ll = 0, rr = w;
  while (ll < rr) {
    long long mm = (ll + rr + 1) >> 1;
    long long need = 0;
    for (int i = (1); i < (18); ++i) {
      long long mi = max(up[i - 1], m);
      long long ma = min(up[i], m + mm);
      if (mi < ma) {
        if (ma - mi > INF / (i * k)) {
          need = INF;
          break;
        }
        need += i * k * (ma - mi);
      }
    }
    if (need > w)
      rr = mm - 1;
    else
      ll = mm;
  }
  cout << ll;
  return 0;
}
