#include <iostream>
using namespace std;

int main() {
    long long N;
    cin >> N;
    int cnt = 0;
    for (int i = 1; i <= N; i++) {
        int num = i;
        bool flag = true;
        bool isGood = true;
        while (num != 0) {
            int a = num % 10;
            num /= 10;
            if (flag) {
                if (a % 2 != 1) {
                    isGood = false;
                    break;
                } 
            } else {
                if (a % 2 != 0) {
                    isGood = false;
                    break;
                }
            }
            flag = !flag;
        }
        if (isGood) cnt++;
    }
    cout << cnt << endl;
    return 0;
}