#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9;
const int dx[] = {0, 1, 0, -1};
const int dy[] = {1, 0, -1, 0};
int S(long long k) {
  int cnt = 0;
  while (k) {
    k /= 10;
    ++cnt;
  }
  return cnt;
}
long long w, m, k;
int main() {
  scanf("%I64d%I64d%I64d", &w, &m, &k);
  long long ans = 0, tmp = 1;
  long long q = S(m), p = q;
  long long maxd = w / k;
  while (p--) tmp *= 10;
  while (true) {
    if ((tmp - m) * q + ans <= maxd) {
      ans += tmp - m;
      maxd -= (tmp - m) * q;
      m = tmp;
      tmp *= 10;
      ++q;
    } else {
      ans += maxd / q;
      break;
    }
  }
  printf("%I64d\n", ans);
  return 0;
}
