import java.util.Scanner;
public class Test {
public static void main(String[] args) {
var scanner = new Scanner(System.in);
var n = scanner.nextInt();
var count = 0;
for (int i = 5, i2 = i * i; i2 <= n; i += 10, i2 = i * i) {
count++;
}
System.out.println(count);
}
}
val n = readln().toFloat()
print((sqrt(n) / 10).roundToInt())