#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <numeric>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <cmath>
#define rep(i, n) for (int64_t i = 0; i < (int64_t)(n); i++)
using namespace std;
int main() {
    double ans = 0;
    int64_t n; cin >> n;
    int64_t a; cin >> a;
    int64_t b; cin >> b;
    vector<int64_t> k(n+1); rep(i, n+1) cin >> k.at(i);
    double memo;
    for (double x = a; x <= b; x++) {
        rep(i ,n+1) {
            memo = double(k[i]/(i+1));
            rep(j ,i+1) memo *= double(x);
            ans += memo;
        }
    }
    cout << ans << endl;
}