#include<bits/stdc++.h>
using namespace std;
bool huiwen(int n)
{
	bool r;
	int x=0;
	int k=n;
	while(n!=0)
	{
		x=x*10+n%10;
		n=n/10;
	}
	if(x==k)
	{
		r=true;
	}
	else
	{
		r=false;
	}
	return r;
}
int main()
{
	int n,cnt=0;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		if(huiwen(i)==true)
		{
			cnt++;
		}
	}
	cout<<cnt;
	return 0;
}
/**************************************************************
	Problem: 1149
	User: wangyuxin
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/