import std.stdio, std.string, std.conv, std.range, std.array, std.algorithm;
import std.uni, std.math, std.container, std.typecons, std.typetuple;
import core.bitop, std.datetime;

void main(){
    auto N = readln.chomp.to!ulong;
    ulong a = 10^^9 + 1;
    ulong M = N / a;
    ulong ans;

    //stderr.writeln(M);

    ulong[10] k = [0, 9, 9, 90, 90, 900, 900, 9000, 9000, 90000];
    //stderr.writeln(k);

    int d = 1;
    while(10^^d <= M){
        ans += k[d];
        ++d;
    }
    --d;
    //stderr.writeln(d);

    int uni = d > 0 ? 10^^d + 1 : 1;
    int e = 1;
    while(10^^d * e <= M){
        //stderr.writeln(uni*e);
        ans += max(1, k[max(0, d - 2)]);
        ++e;
    }
    --e;
    //stderr.writeln(e);

    int f = 1;
    while(uni*e + f*10 <= M){
        if(is_kaibun(f)){
            ++ans;
        }
        ++f;
    }

    writeln(ans);
}

bool is_kaibun(int m){
    int rev, rem, tmp;
    tmp = m;

    while(tmp != 0){
        rem = tmp % 10;
        rev = rev * 10 + rem;
        tmp /= 10;
    }

    if(m == rev) return true;
    else return false;
}


void readVars(T...)(auto ref T args){
    auto line = readln.split;
    foreach(ref arg ; args){
        arg = line.front.to!(typeof(arg));
        line.popFront;
    }
    if(!line.empty){
        throw new Exception("args num < input num");
    }
}