import java.io.*;
import java.math.BigInteger;
import java.util.*;
import java.util.StringTokenizer;
import java.util.function.ToIntBiFunction;

public class Main2 {

    // Mark's Solution

    public static void main(String[] args) throws IOException {
        FastReader fr = new FastReader();
        TreeMap<Long, Duo> cnts = new TreeMap<>();
        PriorityQueue<Duo> duos = new PriorityQueue<>(Comparator.comparingDouble(Duo::a).reversed());

        int N = fr.nextInt();
        long summ = 0;
        double score = 0;
        for (int i = 0; i < N; ++i)
        {
            long pos = fr.nextLong(), wei = fr.nextLong();
            summ += pos * wei;
            cnts.put(pos, new Duo(pos, wei, 1L));
            duos.add(new Duo(pos, wei, 1));
        }
        boolean goingDown = summ >= 0;
        summ = Math.abs(summ);

        while (summ != 0)
        {
            Duo duo = duos.poll();
            if (!cnts.containsKey(duo.pos) || cnts.get(duo.pos).cnt != duo.cnt)
                continue;
            cnts.remove(duo.pos);

            Long target = goingDown ? cnts.lowerKey(duo.pos) : cnts.higherKey(duo.pos);

            double diff = (double) summ / duo.weight;
            if (target != null && Math.abs(duo.pos - target) < diff)
            {
                summ -= Math.abs(duo.pos - target) * duo.weight;
                score += Math.abs(duo.pos - target) * duo.cnt;

                Duo newDuo = new Duo(target, cnts.get(target).weight + duo.weight, cnts.get(target).cnt + duo.cnt);
                cnts.put(target, newDuo);
                duos.add(newDuo);

                continue;
            }
            score += diff * duo.cnt;
            break;
        }

        System.out.println(score);
    }

    static class Duo
    {
        long pos;
        long weight;
        long cnt;

        public Duo (long p, long w, long c)
        {
            this.pos = p;
            this.weight = w;
            this.cnt = c;
        }

        public double a() {return (double) weight / cnt;}
    }

    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() throws IOException {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
            //br = new BufferedReader(new FileReader("D:\\Coding\\ICPC\\pp-naq20251011\\Problems\\seesaw\\data\\secret\\max_1.in"));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            st = null;
            return str;
        }
    }

}