#include<bits/stdc++.h>
#define int long long
using namespace std;
const int M=1e9+1;
signed main(){
	int n,ans=0;cin>>n;
	//1000000001 1000000001
	for(int i=1;i<=10000;i++){
		string a,a1,b;a1=a=b=to_string(i);
		reverse(b.begin(),b.end());a=a+b;
		for(int i=1;i<b.size();i++)a1+=b[i];
		int s1=stoi(a1);if(s1*M>n)break;ans++;
		int s=stoi(a);if(s*M<=n)ans++;
	}cout<<ans;
	return 0;
}