import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		double p = sc.nextDouble();
		sc.close();

		double[] dp = new double[1000000];
		dp[0] = 1;
		for (int i = 1; i < dp.length; i++) {
			dp[i] = dp[i - 1] * p;
		}

		double ans = 0;
		double sum = 1;
		for (int i = 1; i < dp.length; i++) {
			ans += i * dp[i];
			sum += dp[i];
		}
		System.out.println(ans / sum);
	}
}