#include<bits/stdc++.h>

using namespace std;

double logC(int n, int k) {
    return lgamma(n + 1) - lgamma(k + 1) - lgamma(n - k + 1);
}

double negative_binomial_pmf(int k, int r, double p) {
    if (k < r) return 0.0;
    double log_pmf = logC(k - 1, r - 1) + r * log(p) + (k - r) * log(1 - p);
    return exp(log_pmf);
}

double negative_binomial_cdf(int k, int r, double p) {
    double cdf = 0.0;
    for (int i = r; i <= k; i++) {
        cdf += negative_binomial_pmf(i, r, p);
    }
    return cdf;
}

int main() {
    int n, l, r;
    double p;
    cin >> n >> p >> l >> r;
    double expected = 0.0;
    for (int i = 1; i <= n; i++) {
        double prob_l = negative_binomial_cdf(l - 1, i, p);
        double prob_r = negative_binomial_cdf(r, i, p);
        expected += prob_r - prob_l;
    }
    cout <<fixed<<setprecision(10)<< expected << endl;
    return 0;
}