import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        long initial = scanner.nextLong();
        long nextToInitial = 0;

        int counter = 0;

        while (true) {
            nextToInitial = factorial(counter);

            if (initial < nextToInitial) {
                break;
            }

            counter++;
        }

        System.out.println(counter);
    }

    public static long factorial(int n) {
        if (n == 0) {
            return 1;
        }

        return n * factorial(n - 1);
    }
}