#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;
    });

    
    tp = sump, fp = sumn;
    vector<pii> ans;
    ans.push_back({tp, fp});

    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;
    }

    ll Ans = 0, maxn = 0, lst = 0;

    
    sort(ans.begin(), ans.end(), [&](pii x, pii y){
        if(x.second == y.second) return x.first < y.first;
        return x.second < y.second;
    });


    for(int i = 0, j; i < ans.size(); ++i) {
        maxn = max(maxn, ans[i].first);
        Ans += maxn * (ans[i].second - lst);
        lst = ans[i].second;
    }

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

int main(){
    ios::sync_with_stdio(0), cin.tie(0);
    slv();
    return 0;
}
/*
6
+ 7
- 2
- 5
+ 4
- 2
+ 6
*/
/*
3
+ 2
- 3
- 1
*/
/*
8
+ 34
+ 33
+ 26
- 34
- 38
+ 39
- 7
- 27
*/