#ifndef LOCAL
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma GCC diagnostic ignored "-Wpedantic"
#endif
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
auto seed = chrono::high_resolution_clock::now().time_since_epoch().count();
mt19937 rnd(52);
template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T, typename V>
using table = gp_hash_table<T, V>;
using i128 = __int128;
using ll = long long;
using ld = long double;
using uint = unsigned int;
using ull = unsigned long long;
const ll INF = 2e18;
const int inf = 2e9;
const int maxn = 1e5;
const int MOD = 988244353;
const ld pi = acos(-1);
const int P = 5167;
const int L = 26;
const ld EPS = 1e-7;
template<typename T, typename V>
void fill(T &container, V value) {
for (auto &c: container)
c = value;
}
#define int ll
void solve() {
int n;
cin >> n;
vector<ld> a(n), b(n);
for (int i = 0; i < n; ++i) {
cin >> a[i] >> b[i];
}
sort(a.rbegin(), a.rend());
sort(b.rbegin(), b.rend());
vector<ld> pref_a(n + 1), pref_b(n + 1);
for (int i = 0; i < n; ++i) {
pref_a[i + 1] = pref_a[i] + a[i];
pref_b[i + 1] = pref_b[i] + b[i];
}
ld ans = 0;
for (int x = 0; x <= n; ++x) {
int y = lower_bound(pref_b.begin(), pref_b.end(), pref_a[x]) - pref_b.begin();
ans = max(ans, pref_a[x] - (x + y));
}
swap(pref_a, pref_b);
cout << ans;
}
signed main() {
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout << fixed << setprecision(4);
int t = 1;
//cin >> t;
while (t--) solve();
//stress();
}
