#include "bits/stdc++.h"
#define REP(i,n,N) for(ll i=(n); i<(N); i++)
#define RREP(i,n,N) for(ll i=(N-1); i>=n; i--)
#define CK(n,a,b) ((a)<=(n)&&(n)<(b))
#define ALL(v) (v).begin(),(v).end()
#define p(s) cout<<(s)<<endl
#define p2(a,b) cout<<(a)<<" "<<(b)<<endl
#define v2(T) vector<vector<T>>
typedef long long ll;
using namespace std;
const ll mod= 1e10;

int main(){
    ll N,ans=0;
    cin>>N;
    if(N<1e9+1){
        p(0);
        return 0;
    }

    for(ll i=1;i<=101000;i++){
        string s = to_string(i);
        int n = s.size();
        ll x = 0;
        REP(i, 0, n - 1) x = x * 10 + s[i] - '0';
        x = x * 10 + s[n - 1] - '0';
        REP(i, 0, n - 1) x = x * 10 + s[n - 2 - i] - '0';

        ll a = x;
        REP(i, 0, 9) a *= 10;
        a += x;

        if (0 <= a && a <= N) ans++;

        ll xx = 0;
        REP(i, 0, n) xx = xx * 10 + s[i] - '0';
        REP(i, 0, n) xx = xx * 10 + s[n - 1 - i] - '0';

        ll b = xx;
        REP(i, 0, 9) b *= 10;
        b += xx;

        if (0 <= b && b <= N) ans++;
    }
    p(ans);
    return 0;
}