#include <bits/stdc++.h>
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
typedef long long ll;
typedef pair<ll, ll> pll;
const ll INF = 0x3f3f3f3f;
const ll MO9 = 998244353;
const ll MO1 = 1e9 + 7;
const ll MO = MO9;
const int N = 5e5 + 5;
ll n, m;
ll s[N];
long double p[N];
struct node {
  long double p;
  ll c;
} a[N], b[N];
void solve() {
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> b[i].p >> b[i].c;
  sort(b + 1, b + n + 1, [=](node a, node b) { return a.p > b.p; });
  int t = 0;
  b[0].p = -1.0;
  for (int i = 1; i <= n; i++) {
    if (b[i].p == b[i - 1].p) {
      a[t].c += b[i].c;
    } else
      a[++t] = b[i];
  }
  n = t;
  for (int i = 1; i <= n; i++) {
    // cin>>s[i];
    s[i] = a[i].c;
    s[i] += s[i - 1];
    p[i] = a[i].p;
  }
  long double ans = 0;
  for (int i = 1; i <= n; i++) {
    long double tot = 1.0 * s[i] / p[i];
    // cout<<tot<<'\n';
    int res = n;
    int l = i + 1, r = n;
    while (l <= r) {
      int mid = l + r >> 1;
      if (1.0 * (s[n] - s[mid - 1]) <= tot * (1.0 - p[mid])) {
        res = mid;
        ans = max(ans, s[n] - s[mid - 1] + s[i] - tot);
        r = mid - 1;
      } else
        l = mid + 1;
    }
  }
  cout << fixed << setprecision(9) << ans << '\n';
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
  int ttt = 1;
  // cin>>ttt;
  while (ttt--) solve();
  return 0;
}