#include<bits/stdc++.h>
using namespace std;
int t(int n)
{
    int t = 0;
    while (n!=0)
    {
        t = t * 10 + n % 10;
        n = n / 10;
    }
    return t;
}
int main()
{
    int k;
    int s = 0;
    cin >> k;
    for(int i=1;i<=k;i++)
    {
        if(t(i) == i)
        {
            s+=1;
        }
    }
    cout<<s;
    return 0;
}
/**************************************************************
	Problem: 1149
	User: wuyichen
	Language: C++
	Result: Accepted
	Time:17 ms
	Memory:2072 kb
****************************************************************/