/*#pragma GCC optimize("O3")
#pragma GCC target ("avx2")
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC optimize("unroll-loops")*/
#include <bits/stdc++.h>
#pragma GCC optimize ("unroll-loops,Ofast,O3")
#pragma GCC target("avx,avx2,fma")
//#define file(data) freopen(data".in", "r", stdin); freopen(data".out", "w", stdout);
#define pb push_back
//#define ios ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define all(data) data.begin() , data.end()
#define endl '\n'
//freopen("nenokku_easy.in", "r", stdin);
//freopen("nenokku_easy.out", "w", stdout);
#define int long long
#define pii pair < int, int >
#define pll pair < long long, long long >
using namespace std;
typedef long long ll;
const int N = 2e5 + 5;
const int M = 305;
const int mod = 1e9 + 7;
int n;
double a[N], b[N], pref[N];
main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
//file("pieaters");
cin >> n;
for(int i = 1; i <= n; i++) {
cin >> a[i] >> b[i];
}
sort(a + 1, a + n + 1);
reverse(a + 1, a + n + 1);
sort(b + 1, b + n + 1);
reverse(b + 1, b + n + 1);
for(int i = 1; i <= n; i++) {
pref[i] = pref[i - 1] + b[i];
}
double ans = 0, suma = 0;
for(int i = 1; i <= n; i++) {
suma += a[i];
int l = 1, r = n;
while(r - l > 2) {
int md1 = l + (r - l) / 3, md2 = r - (r - l) / 3;
if(min(suma, pref[md1]) - i - md1 >= min(suma, pref[md2]) - i - md2) {
r = md2;
} else {
l = md1;
}
}
ans = max(ans, min(suma - i - r, pref[r] - i - r));
ans = max(ans, min(suma - i - l, pref[l] - i - l));
l++;
ans = max(ans, min(suma - i - l, pref[l] - i - l));
/*
for(int j = 1; j <= n; j++) {
ans = max(ans, min(suma, pref[j]) - i - j);
}*/
}
cout << fixed << setprecision(4) << ans;
}
