#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

typedef int _loop_int;
#define REP(i,n) for(_loop_int i=0;i<(_loop_int)(n);++i)
#define FOR(i,a,b) for(_loop_int i=(_loop_int)(a);i<(_loop_int)(b);++i)
#define FORR(i,a,b) for(_loop_int i=(_loop_int)(b)-1;i>=(_loop_int)(a);--i)

#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define DEBUG_VEC(v) cout<<#v<<":";REP(i,v.size())cout<<" "<<v[i];cout<<endl
#define ALL(a) (a).begin(),(a).end()

#define CHMIN(a,b) a=min((a),(b))
#define CHMAX(a,b) a=max((a),(b))

// mod
const ll MOD = 1000000007ll;
#define FIX(a) ((a)%MOD+MOD)%MOD

// floating
typedef double Real;
const Real EPS = 1e-11;
#define EQ0(x) (abs(x)<EPS)
#define EQ(a,b) (abs(a-b)<EPS)
typedef complex<Real> P;

set<int> V;

int main(){
  ll x;
  cin>>x;

  ll y = x % 1000000000;
  x /= 1000000000;
  // x以下の回文数
  FOR(i,1,10)V.insert(i);
  FOR(keta,2,10){
    int hf = keta/2;
    int ten = 1;REP(i,hf)ten*=10;
    char yo[hf+1];
    REP(i,hf)yo[i]='0';
    yo[hf-1]='1';
    yo[hf]='\0';
    while(true){
      char po[hf+1];po[hf]='\0';
      REP(i,hf)po[hf-1-i]=yo[i];
      if(keta%2==0){
        V.insert(atoi(po)*ten + atoi(yo));
      }else{
        REP(i,10){
          V.insert(atoi(po)*ten*10 + i*ten + atoi(yo));
        }
      }
      int j = hf-1;
      while(j>=0){
        if(yo[j]=='9'){
          if(j==hf-1)yo[j]='1';
          else yo[j]='0';
          j--;
        }else{
          yo[j]++;
          break;
        }
      }
      if(j==-1)break;
    }
  }
  int ans = 0;
  for(auto yo : V){
    if(yo < x){
      ans++;
    }else if(yo==x){
      if(yo<=y)ans++;
    }
  }
  cout<<ans<<endl;
  return 0;
}