ABC382E

#include <assert.h>
#include <bits/stdc++.h>
using namespace std;
#ifndef __DEBUG__
#define dbg(...) 42
#endif
template <class T>
using mpq = priority_queue<T, vector<T>, greater<T>>;

using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vl = vector<ll>;
using vi = vector<int>;

int main(int argc, char **argv) {
    ll n, x;
    cin >> n >> x;
    vl ps(n);
    for (auto &x : ps)
        cin >> x;

    vector<vector<double>> prob(n, vector<double>(n + 1));  // 一次抽卡, 考虑前i项获得j张卡的概率

    prob[0][0] = 1 - (ps[0] / 100.0);
    prob[0][1] = ps[0] / 100.0;
    for (ll i = 1; i < n; ++i) {
        double p = ps[i] / 100.0;
        prob[i] = prob[i - 1];
        for (auto &v : prob[i])
            v *= (1 - p);

        for (ll j = 1; j <= i + 1; ++j) {
            double pprev = prob[i - 1][j - 1];
            prob[i][j] += pprev * p;
        }
    }

    const auto &pt = prob.back();
    dbg(pt);
    assert(abs(accumulate(pt.begin(), pt.end(), 0.0, std::plus<>()) - 1) < 1e-6);

    vector<double> expect(x + 1);
    auto search = [&](auto &&self, ll v) -> double {
        if (v < 0)
            return 1.0;
        if (expect[v] != 0)
            return expect[v];
        double factor = 1 - pt[0], eacc = 0;
        for (ll i = 1; i <= min(n, v); ++i) {
            eacc += pt[i] * self(self, v - i);
        }
        double full = 0;
        for (ll i = min(n, v); i <= n; ++i) {
            full += pt[i];
        }
        return expect[v] = eacc / factor;
    };

    search(search, x);
    dbg(expect);
    cout << expect[x] << '\n';
    return 0;
};