#include<bits/stdc++.h>
#define int long long
using namespace std;
int n,ans;
signed main(){
//	freopen("palindrome.in","r",stdin);
//	freopen("palindrome.out","w",stdout);
	cin>>n;
	for(int i=1;i<=114514;i++){
		string s,t,str;
		s=t=str=to_string(i);
		reverse(t.begin(),t.end());
		s+=t;
		for(int j=1;j<t.size();j++)str+=t[j];
		if(str.size()>10||(str.size()==10&&str[0]>1))continue;
		int x=stoi(str);
		if(x*1000000001>n)break;
		ans++;
		if(s.size()>10||(s.size()==10&&s[0]>1))continue;
		int y=stoi(s);
		if(y*1000000001<=n)ans++;
	}
	cout<<ans<<endl;
	return 0;
}