#include <bits/stdc++.h>

#ifndef LOCAL_
#define fprintf if( false ) fprintf
#endif // LOCAL_
#define dumpi(x1) fprintf(stderr, "#%s.%d (%s) = (%d)\n", __func__, __LINE__, #x1, x1);
#define dumpii(x1, x2) fprintf(stderr, "#%s.%d (%s, %s) = (%d, %d)\n", __func__, __LINE__, #x1, #x2, x1, x2);
#define dumpiii(x1, x2, x3) fprintf(stderr, "#%s.%d (%s, %s, %s) = (%d, %d, %d)\n", __func__, __LINE__, #x1, #x2, #x3, x1, x2, x3);
#define dumpl(x1) fprintf(stderr, "#%s.%d (%s) = (%ld)\n", __func__, __LINE__, #x1, x1);
#define dumpll(x1, x2) fprintf(stderr, "#%s.%d (%s, %s) = (%ld, %ld)\n", __func__, __LINE__, #x1, #x2, x1, x2);
#define dumpd(x1) fprintf(stderr, "#%s.%d (%s) = (%lf)\n", __func__, __LINE__, #x1, x1);
#define dumpdd(x1, x2) fprintf(stderr, "#%s.%d (%s, %s) = (%lf, %lf)\n", __func__, __LINE__, #x1, #x2, x1, x2);

template<typename T>
T pow(T x, long n) {
  T res = 1;
  T p = x;
  while( n != 0 ) {
    if( n & 0x01 ) res *= p;
    p *= p;
    n >>= 1;
  }
  return res;
}

// 135 --f-> ys[0] = 5, ys[1] = 3, ys[2] = 1, return = 3
// 121 --g-> true
// 123 --g-> false
// 343 --g-> false
struct Library0002 {
  long x;
  long len;
  long xs[32];
  Library0002(long x_) : x(x_), len(0) {
    while( x != 0 ) {
      xs[len] = x % 10;
      x /= 10;
      len += 1;
    }
  }
  long f(long *ys) {
    for(int i = 0; i < len; ++i) {
      ys[i] = xs[i];
    }
    return len;
  }
  bool g() {
    for(int i = 0; i < len; ++i) {
      if( xs[i] != xs[len-i-1] ) return false;
    }
    return true;
  }
};

struct Library0001 {
  long xs[32];
  long pr;
  long x;
  Library0001(long x_) : x(x_) {
    pr = x;
    xs[0] = 0;
    xs[1] = xs[2] = 9;
    for(int i = 3; i < 32; ++i) {
      xs[i] = xs[i-2] * 10;
    }
    long t = 0;
    for(int i = 0; i < 32; ++i) {
      t += xs[i];
      xs[i] = t;
    }
  }
  long ys[32];
  long m;
  long solve() {
    if( x == 0 ) return 1;
    std::string str = std::to_string(x);
    for(int i = 0; i < (int)str.size(); ++i) {
      ys[i] = str[i] - '0';
    }
    m = (int)str.size();
    long res = 1 + g() + xs[m-1];
    return res + f(0, (m + 1) / 2);
  }
  long g() {
    for(long i = 0; i < m; ++i) {
      long t1 = ys[i];
      long t2 = ys[std::min(i, m - i - 1)];
      if( t1 == t2 ) continue;
      if( t1 <  t2 ) return -1;
      return 0;
    }
    return 0;
  }
  long f(int i, int n) {
    if( n == 0 ) return 0;
    if( n == 1 ) return ys[i] + ((i == 0) ? 0 : 1);
    return pow(10, n - 1) * (ys[i] - ((i == 0) ? 1 : 0)) + f(i + 1, n - 1); 
  }
  long greedy() {
    long res = 0;
    for(long i = 0; i <= x; ++i) {
      if( not check(i) ) continue;
      res += 1;
    }
    return res;
  }
  static bool check(long x) {
    return Library0002(x).g();
  }
  static bool test() {
    bool res = true;
    int count = 0;
    for(long i = 1; i < 10000; ++i) {
      long t1 = Library0001(i).solve();
      long t2 = Library0001(i).greedy();
      if( t1 != t2 ) {
        fprintf(stderr, "solve(%ld) = %ld, greedy(%ld) = %ld\n", i, t1, i, t2);
        res = false;
        count += 1;
        if( count > 30 ) break;
      }
    }
    return res;
  }
};

int main() {
  // if( not Library0001::test() ) return 1;
  
  long n;
  scanf("%ld", &n);
  if( n < 1000000001 ) {
    puts("0");
    return 0;
  }  
  long low  = n % 1000000000;
  long high = n / 1000000000;
  Library0001 lib(high);
  long res = lib.solve() - 1 - ((lib.check(high) and high > low) ? 1 : 0);
  printf("%ld\n", res);
  
  return 0;
}