#include <bits/stdc++.h>
using namespace std;
#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define mp(a,b) make_pair((a),(b))
#define pb(a) push_back((a))
#define all(x) (x).begin(),(x).end()
#define uniq(x) sort(all(x)),(x).erase(unique(all(x)),end(x))
#define fi first
#define se second
#define dbg(x) cout<<#x" = "<<((x))<<endl
template<class T,class U> ostream& operator<<(ostream& o, const pair<T,U> &p){o<<"("<<p.fi<<","<<p.se<<")";return o;}
template<class T> ostream& operator<<(ostream& o, const vector<T> &v){o<<"[";for(T t:v){o<<t<<",";}o<<"]";return o;}

#define INF 2147483600
#define XXX 1000000001

long a[5];
long n;
int res=0;

void exec(int d, int t, long p){
  // 固定深さ，いまの深さ，いまの値
  if(t==d){
    if(p!=0 && p*XXX<=n) res++;
    return;
  }
  if((d-1)/2 < t){
    exec(d, t+1, p*10 + a[d-t-1]);
  } else {
    rep(i,10){
      if(t==0 && i==0) continue;
      a[t]=i;
      exec(d, t+1, p*10 + i);
    }
  }
}

int main(){
  cin>>n;

  rep(i,9) exec(i+1,0,0);

  cout<<res<<endl;

  return 0;
}