#include <bits/stdc++.h>
using namespace std;
const long long INF = 100000000000000000LL;
long long w, M, k;
long long ans;
long long calcS(long long x) {
  if (x < 10) return x;
  long long ret = 0;
  long long i = 1, bit = 1;
  for (; i * 10 <= x; i *= 10, ++bit) ret += bit * i * 9;
  long long digit = x / i % 10;
  ret += (digit - 1) * i * bit;
  ret += (x % i + 1) * bit;
  return ret;
}
int main() {
  cin >> w >> M >> k;
  for (long long l = 0, r = INF - M; l <= r;) {
    long long m = (l + r) / 2;
    if ((calcS(M + m - 1) - calcS(M - 1)) <= w / k)
      ans = m, l = m + 1;
    else
      r = m - 1;
  }
  cout << ans << endl;
  return 0;
}
