/* -*- coding: utf-8 -*-
 *
 * 1849.cc:  No.1849 Three Times Value - yukicoder
 */

#include<cstdio>
#include<algorithm>
 
using namespace std;

/* constant */

/* typedef */

typedef long long ll;

/* global variables */

/* subroutines */

/* main */

int main() {
  ll n;
  scanf("%lld", &n);

  int k = 0;
  for (ll m = n; m > 0; m /= 10) k++;
  //printf("k=%d\n", k);

  int l = k / 3, r = k % 3;
  if (l == 0) { puts("0"); return 0; }

  ll t = 1;
  for (int i = 0; i < l; i++) t *= 10;

  ll x;
  if (r == 0) {
    x = n;
    for (int i = k; i > l; i--) x /= 10;
  }
  else {
    x = 0;
    for (int i = 0; i < l; i++) x = x * 10 + 9;
  }

  if (x * (t * t + t + 1) > n) x--;
  printf("%lld\n", x);
  return 0;
}