#include <bits/stdc++.h>

struct Value {
    char sig;
    int val;
};

void solve() {
    int n;
    std::cin >> n;

    std::vector<Value> a(n + 1, {'*', 0});
    for (int i = 1; i <= n; i++) {
        std::cin >> a[i].sig >> a[i].val;
    }
    std::sort(a.begin() + 1, a.end(), [&](Value x, Value y) {
        return x.val < y.val;
    });

    int tp = 0, fp = 0, tn = 0, fn = 0;
    for (int i = 1; i <= n; i++) {
        if (a[i].sig == '+') tp++;
        else if (a[i].sig == '-') tn++;
    }
    double last = 1;
    double ans = 0;
    for (int i = n; i >= 1; i--) {
        double rate = 1.0 * tp / (tp + fn);
        if (a[i].sig == '+') tp--, fn++;
        else if (a[i].sig == '-') tn--, fp++;
        double cur = 1.0 * fp / (tn + fp);
        ans += rate * (last - cur);
        last = cur;
    }
    std::cout << std::fixed << std::setprecision(12) << ans << '\n';

}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr), std::cout.tie(nullptr);

    int T = 1;
    while (T--) {
        solve();
    }
    return 0;
}