#include<bits/stdc++.h>
using namespace std;
bool hw(int n){
	bool r=false;
	int s=0,x=n;
	while(n!=0){
		s=s*10+n%10;
		n=n/10;
	}
	if(s==x) r=true;
	else r=false;
	return r; 
}
int main(){
    int n,c=0;
    cin>>n;
    for(int i=1;i<=n;i++){
    	if(hw(i)) c++;
	}	
    cout<<c;
	return 0;
}

































































































/**************************************************************
	Problem: 1149
	User: zhuanghaoxiang
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/