import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;

public class Jorke {
    public static void main(String[] args) throws IOException {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
            new Jorke().run(new Scanner(reader));
        }
    }

    public void run(Scanner sc) throws IOException {
        int c = sc.nextInt();
        long t = sc.nextLong(), r = sc.nextLong();
        double p = sc.nextDouble();

        double epsilon = 0.000000001;
        double[][] DP = new double[c + 1][c + 1];
        for (int x = 1; x <= c; x++) {
            double[] row = new double[c + 1];
            double low = epsilon;
            double upp = 1e18;
            while (upp - low > epsilon && upp / low > 1 + epsilon) {
                double mid = (low + upp) / 2;
                for (int y = 1; y < x; y++) {
                    row[y] = Math.min(1 + p * (r + mid) + (1 - p) * row[y - 1], t + DP[y][y]);
                }
                row[x] = 1 + p * (r + mid) + (1 - p) * row[x - 1];
                if (row[x] > mid)
                    low = mid;
                else
                    upp = mid;
            }
            DP[x] = row;
        }
        System.out.println(DP[c][c] + t);
    }
}