#include<bits/stdc++.h>
#define endl '\n'
#define ll long long
#define pii pair<ll, ll>
const ll inf = 2e18;
const double eps = 1e-9;
using namespace std;
void slv(){
    ll n; cin >> n;
    vector<pii> a(n + 1);
    for(int i = 1; i <= n; ++i) {
        ll x; string s;
        cin >> s >> x;
        a[i] = {s[0] == '+' ? 1 : -1, x};
    }

    ll sump = 0, sumn = 0, tp = 0, fp = 0;
    for(int i = 1; i <= n; ++i) {
        if(a[i].first == 1) {
            sump ++;
        } else {
            sumn++;
        }
    }

    sort(a.begin() + 1, a.end(), [&](pii x, pii y) {
        return x.second < y.second;
    });

    
    vector<pii> ans;
    ans.push_back({0, 0});

    for(int i = 1, j; i <= n; ++i) {
        for(j = i; j <= n && a[j].second == a[i].second; ++j);
        --j;

        for(int k = i; k <= j; ++k) {
            if(a[k].first == 1) tp++; 
            if(a[k].first == -1) fp++;
        }

        ans.push_back({tp, fp});
        i = j;
    }

    // cout << "ok" << endl;
    ll Ans = 0;
    ll maxn = 0.0, lst = 0.0;
    sort(ans.begin(), ans.end(), [&](pii x, pii y){
        return x.second < y.second;
    });

    for(auto [p, f]: ans) {
        maxn = max(maxn, p);
        Ans += maxn * (f - lst);
        lst = f;
    }

    cout << fixed << setprecision(14) << ((long double)0.0 + sump * sumn - Ans) / (sump * sumn) << endl;
}

int main(){
    //ios::sync_with_stdio(0), cin.tie(0);
    int _ = 1;
    //cin >> _;
    while(_--) slv();
    return 0;
}