#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<=100000;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];
		if(a1.size()>10||a1.size()==10&&a1[0]>1)continue;
		int s1=stoi(a1);
		if(s1*M>n)break;
		ans++;if(a.size()>10||a.size()==10&&a[0]>1)continue;
		int s=stoi(a);
		if(s*M<=n)ans++;//cout<<s<<' '<<s1<<'\n';
	}
	cout<<ans;
	return 0;
}