#include<iostream>
using namespace std;
int jud(int a) {int c = 1;//位数while (a) {int t = a % 10;if (c % 2 != 0) {//奇数位if (t % 2 == 0)return 0;//偶数不符合}else {//偶数位if (t % 2 != 0)return 0;//奇数不符合}c++;a /= 10;}return 1;
}
int main() {int count = 0;int n;cin >> n;for (int i = 1; i <= n; i++) {if (i % 2 != 0) {if (jud(i))count++;}}cout << count << endl;return 0;
}