import std;
class Reader {
    DList!(string) buf;

    private void readNext() {
        while (buf.empty) {
            auto inputs = stdin.readln()[0 .. $ - 1].split(" ");
            foreach (token; inputs) {
                buf.insertBack(token);
            }
        }
    }

    void read()() {

    }

    void read(T, A...)(ref T t, ref A a) {
        if (buf.empty) {
            readNext();
        }
        static if (is(T == char[])) {
            string token = buf.front();
            t = token.dup;
            buf.removeFront();
        } else static if (isArray!(T)) {
            foreach (ref v; t) {
                read(v);
            }
        } else {
            t = buf.front.to!T;
            buf.removeFront();
        }
        read(a);
    }
}

ref auto chmin(T)(ref T a, T b) {
    if (a > b) {
        a = b;
    }
    return a;
}

ref auto chmax(T)(ref T a, T b) {
    if (a < b) {
        a = b;
    }
    return a;
}

public const int INF = 1 << 30;
public const long LINF = 2e18.to!long;

void main() {
	Reader reader = new Reader();
	int N;
	reader.read(N);
	alias T = Tuple!(int, char);
	T[] V = new T[N];
	int neg = 0, pos = 0;
	foreach (i; 0 .. N) {
		char C;
		int X;
		reader.read(C, X);
		if (C == '+')
			pos++;
		else
			neg++;
		V[i] = T(X, C);
	}
	V.sort();
	int fn = 0;
	int tp = pos;
	double ans = 0;
	foreach (t; V) {
		char c;
		int x;
		AliasSeq!(x, c) = t;
		if (c == '-') {
			ans += double(1) / neg * tp / pos;
		} else {
			tp--;
		}
	}
	writef("%.10f\n", ans);
}