#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <cassert>
#include <cmath>
using namespace std;
struct Book {
double t, r;
};
// state: 0 => skip, 1 => bet T1 (chi 1 đồng, nhận t_i nếu T1 thắng), 2 => bet RNG (chi 1 đồng, nhận r_i nếu RNG thắng)
double calcGuarantee(const vector<Book>& books, const vector<int>& state) {
double sumT1 = 0.0, sumRNG = 0.0;
int cost = 0;
int n = books.size();
for (int i = 0; i < n; i++) {
if(state[i] == 1) {
sumT1 += books[i].t;
cost++;
} else if(state[i] == 2) {
sumRNG += books[i].r;
cost++;
}
}
double profitT1 = sumT1 - cost;
double profitRNG = sumRNG - cost;
return min(profitT1, profitRNG);
}
int main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n;
cin >> n;
vector<Book> books(n);
for (int i = 0; i < n; i++){
cin >> books[i].t >> books[i].r;
}
double bestGuarantee = -1e9;
int total = 1;
for (int i = 0; i < n; i++) total *= 3;
for (int mask = 0; mask < total; mask++) {
int tmp = mask;
vector<int> state(n, 0);
for (int i = 0; i < n; i++) {
state[i] = tmp % 3; // 0,1,2
tmp /= 3;
}
double cur = calcGuarantee(books, state);
bestGuarantee = max(bestGuarantee, cur);
}
cout << fixed << setprecision(4) << bestGuarantee << "\n";
return 0;
}
