#include <bits/stdc++.h>
using namespace std;
#define all(x) x.begin(), x.end()
#define ar array
#define pb push_back
#define ln '\n'
#define int long long
using i64 = long long;
template <class F, class _S>
bool chmin(F &u, const _S &v){
bool flag = false;
if ( u > v ){
u = v; flag |= true;
}
return flag;
}
template <class F, class _S>
bool chmax(F &u, const _S &v){
bool flag = false;
if ( u < v ){
u = v; flag |= true;
}
return flag;
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n; cin >> n;
using ld = long double;
vector <ld> a, b;
for ( int i = 0; i < n; i++ ){
ld x, y; cin >> x >> y;
a.pb(x), b.pb(y);
}
sort(all(a), greater <ld> ());
sort(all(b), greater <ld> ());
n = a.size();
int m = b.size();
vector <ld> pf(m + 1), mx(m + 1);
for ( int i = 0; i < m; i++ ){
pf[i + 1] = pf[i] + b[i];
mx[i + 1] = max(mx[i], pf[i + 1] - (i + 1));
}
auto ok = [&](ld x){
ld s = 0;
for ( int i = 0; i <= n; i++ ){
if ( s - i >= x ){
int j = max(0LL, (int)floor(s - x - i));
chmin(j, m);
if ( mx[j] - i >= x ){
return true;
}
}
if ( i < n ){
s += a[i];
}
} return false;
};
ld l = 0, r = 1e12;
for ( int _ = 0; _ <= 100; _++ ){
ld md = (l + r) / 2;
if ( ok(md) ) l = md;
else r = md;
}
cout << fixed << setprecision(4) << l;
cout << '\n';
}
