#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>
using namespace std;
/**
* CEOI 2017 - Sure Bet
* Vaqt murakkabligi: O(N log N) - saralash tufayli
* Xotira murakkabligi: O(N) [cite: 4]
*/
int main() {
// Kirish va chiqishni tezlashtirish
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n;
if (!(cin >> n)) return 0; // Bukmekerlar sonini o'qish [cite: 19, 43]
vector<double> a(n), b(n);
for (int i = 0; i < n; i++) {
cin >> a[i] >> b[i]; // a_i va b_i koeffitsientlarini o'qish [cite: 19, 45, 46, 47, 48]
}
// Eng katta koeffitsientlarni olish uchun har bir natijani alohida saralaymiz
sort(a.rbegin(), a.rend());
sort(b.rbegin(), b.rend());
double max_profit = 0.0;
double sum_a = 0.0;
double sum_b = 0.0;
int ptr_b = 0;
// 1-natija uchun tikilgan tikishlar sonini (i) oshirib boramiz [cite: 14]
for (int i = 0; i <= n; i++) {
if (i > 0) sum_a += a[i - 1];
// 2-natija uchun summani (sum_b) muvozanatlashtirish uchun ptr_b ni suramiz [cite: 15, 51]
while (ptr_b < n) {
double current_profit = min(sum_a, sum_b + b[ptr_b]) - (i + ptr_b + 1);
// Agar yangi tikish qo'shish foydani oshirsa yoki muvozanatni yaxshilasa
if (sum_b + b[ptr_b] < sum_a) {
sum_b += b[ptr_b];
ptr_b++;
max_profit = max(max_profit, min(sum_a, sum_b) - (i + ptr_b));
} else {
// Agar sum_b sum_a dan o'tib ketsa, bu nuqtada ham foydani tekshirib to'xtaymiz
max_profit = max(max_profit, min(sum_a, sum_b + b[ptr_b]) - (i + ptr_b + 1));
break;
}
}
// Har bir qadamda kafolatlangan foydani yangilab boramiz
max_profit = max(max_profit, min(sum_a, sum_b) - (i + ptr_b));
}
// Natijani verguldan keyin 4 ta raqam bilan chiqarish [cite: 34, 36]
cout << fixed << setprecision(4) << max_profit << endl;
return 0;
}
