#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>

#include <functional>
#include <cassert>

typedef long long ll;
using namespace std;

#define debug(x) cerr << #x << " = " << (x) << endl;


#define mod 1000000007 //1e9+7(prime number)
#define INF 1000000000 //1e9
#define LLINF 2000000000000000000LL //2e18
#define SIZE 100010


int main(){
  ll n;
  set<ll> mm;
  scanf("%lld",&n);

  int m = n/1000000000;

  int ans = 0;
  
  for(int i=0;i<m;i++){
    int p = i;

    char s1[20],s1_r[20],s2[20];

    sprintf(s1_r,"%d",p);
    reverse(s1_r,s1_r+strlen(s1_r));
    
    sprintf(s1,"%d%s",p,s1_r);
    sprintf(s2,"%d%s",p/10,s1_r);

    ll q1 = atoll(s1);    
    ll q2 = atoll(s2);

    //debug(q1);
    //debug(q2);
    
    if(q1 <= m && mm.find(q1) == mm.end()){
      mm.insert(q1);
      ans++;
    }

    if(q2 <= m && mm.find(q2) == mm.end()){
      mm.insert(q2);
      ans++;
    }

    if(q1 >= 10000000000LL) break;
  }
  
  cout << ans-1 << endl;
  
  return 0;
}