#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;

vector<long double> p;
vector<ll> c;
int n;
const long double EPS = 1e-10L;
long double f(long double x, long double y)
{
    ll sx = 0, sy = 0;
    for (int i = 1; i <= n; ++i)
        if (p[i] * x >= 1)
            sx += c[i];
        else if ((1 - p[i]) * y >= 1)
            sy += c[i];
    // cout << sx << ' ' << sy << ' ' << x << ' ' << y << ' ' << sx + sy - max(sx * x, sy * y) << '\n';
    return sx + sy - max(sx * x, sy * y);
}
long double get(long double x)
{
    long double l = 0, r = 2000000;
    long double lans = f(x, l), rans = f(x, r);
    long double ans = max(lans, rans);
    for (int _ = 0; _ < 100; ++_) {
        long double lmid = l + (r - l) / 3;
        long double rmid = r - (r - l) / 3;

        lans = f(x, lmid), rans = f(x, rmid);
        ans = max(lans, rans);
        if (lans - rans >= EPS)
            r = rmid;
        else
            l = lmid;
    }
    // cout << x << ' ' << l << ' ' << ans << '\n';
    return ans;
}
void solve()
{
    cin >> n;
    p.resize(n + 5);
    c.resize(n + 5);
    for (int i = 1; i <= n; ++i)
        cin >> p[i] >> c[i];

    long double l = 0, r = 2000000;
    long double lans = get(l), rans = get(r);
    long double ans = max(lans, rans);
    for (int _ = 0; _ < 100; ++_) {
        long double lmid = l + (r - l) / 3;
        long double rmid = r - (r - l) / 3;

        lans = get(lmid), rans = get(rmid);
        ans = max(lans, rans);
        if (lans - rans >= EPS)
            r = rmid;
        else
            l = lmid;
    }
    // cout << f(1 / .6L, 1.9) << '\n';
    // cout << get(1 / .6L) << '\n';
    cout << fixed << setprecision(10) << ans << '\n';
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int T = 1;
    while (T--)
        solve();
    return 0;
}