#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: chenmingyu
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/