#include <bits/stdc++.h>
#define fi first
#define se second
using namespace std;
const int N = 1e5;
int n;
double a[2][N + 2], pref[2][N + 2], ans = 0;
void input() {
cin >> n;
for(int i = 1; i <= n; i++) {
cin >> a[0][i] >> a[1][i];
}
}
void solve() {
sort(a[0] + 1, a[0] + n + 1, greater<double>());
sort(a[1] + 1, a[1] + n + 1, greater<double>());
// for(int i = 1; i <= n; i++) cout << a[0][i] << " ";
// cout << '\n';
// for(int i = 1; i <= n; i++) cout << a[1][i] << " ";
// cout << '\n';
for(int i = 1; i <= n; i++) {
pref[0][i] = pref[0][i - 1] + a[0][i];
pref[1][i] = pref[1][i - 1] + a[1][i];
}
for(int x = 0; x <= 1; x++) {
double cur = 0;
int cnt = 0;
for(int i = 1; i <= n; i++) {
cnt++;
cur += a[x][i];
if(cur - cnt < 0) continue;
int l = 0, r = n;
while(r - l > 1) {
int mid = (l + r) >> 1;
int cost = cnt + mid;
if(cur - cost < 0) r = mid;
else {
if(cur - cost <= pref[x ^ 1][mid] - cost) {
l = mid;
} else r = mid;
}
}
// cout << i << " " << l << '\n';
if(l > 0) ans = max(ans, cur - cnt - l);
}
}
cout << fixed << setprecision(4) << ans;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
//freopen(" .inp", "r", stdin);
//freopen(" .out", "w", stdout);
input();
solve();
return 0;
}
