#include <bits/stdc++.h>
using namespace std;

#define fi first
#define se second
#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define each(itr,v) for(auto itr:v)
#define pb(s) push_back(s)
#define mp(a,b) make_pair(a,b)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl
#define maxch(x,y) x=max(x,y)
#define minch(x,y) x=min(x,y)
#define uni(x) x.erase(unique(all(x)),x.end())
#define exist(x,y) (find(all(x),y)!=x.end())
#define bcnt(x) bitset<32>(x).count()

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef pair<P, int> PPI;
typedef pair<ll, ll> PL;
typedef pair<P, ll> PPL;

#define INF INT_MAX/3

#define MAX_N 1000

bool isp(string s){
  int n=s.length();
  rep(i,n/2)if(s[i]>s[n-i-1])return false;
  return true;
}

ll rec(string n,ll nd,ll digit,bool flag){
  if(nd>digit/2+digit%2)return (flag==true||isp(n)==true?1:0);
  if(flag)return 10*rec(n,nd+1,digit,flag);
  ll res=0;
  ll maxd=n[nd-1]-'0';
  for(ll i=0;i<=maxd;i++){
    if(nd==1&&i==0)continue;
    res+=rec(n,nd+1,digit,i<maxd);
  }
  return res;
}

ll n;
ll res=0;

int main(){
	cin.sync_with_stdio(false);
  cin>>n;
  n/=1000000001;
  ll digit=1;
  for(ll x=1;x<=n;x*=10){
    res+=rec(to_string(min(x*10-1,n)),1LL,digit++,false);
  }
  cout<<res<<endl;
	return 0;
}