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

int main() {
    ll n;
    cin>>n;
    n/=1000000001;
    int ans=0;
    for (int i=1;i<100000;i++) {
        string s=to_string(i);
        int len=s.size();
        string t=s;
        for (int j=len-1;j>=0;j--)
            t+=s[j];
        if (stoll(t)<=n)
            ans++;
        t=s;
        for (int j=len-2;j>=0;j--)
            t+=s[j];
        if (stoll(t)<=n)
            ans++;
    }
    cout<<ans<<endl;
    return 0;
}