#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;
#define endl '\n'
#define fi first
#define se second
#define For(i, l, r) for (auto i = (l); i < (r); i++)
#define ForE(i, l, r) for (auto i = (l); i <= (r); i++)
#define FordE(i, l, r) for (auto i = (l); i >= (r); i--)
#define Fora(v, a) for (auto v: (a))
#define bend(a) (a).begin(), (a).end()
#define isz(a) ((signed)(a).size())
using ll = long long;
using ld = long double;
using pii = pair <int, int>;
using vi = vector <int>;
using vpii = vector <pii>;
using vvi = vector <vi>;
const int N = 1e5 + 5;
int n;
int a[N], b[N];
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
// freopen("KEK.inp", "r", stdin);
// freopen("KEK.out", "w", stdout);
cin >> n;
ForE(i, 1, n){
double x, y; cin >> x >> y;
a[i] = round(x * 10000); b[i] = round(y * 10000);
}
sort(a + 1, a + n + 1); reverse(a + 1, a + n + 1);
sort(b + 1, b + n + 1); reverse(b + 1, b + n + 1);
ll ans = 0;
{
ll suma = 0, sumb = 0;
int idx = 0;
ForE(i, 1, n){
suma += a[i];
while (idx + 1 <= n and sumb < suma){
idx++;
sumb += b[idx];
}
ans = max(ans, min(suma, sumb) - (ll)(i + idx) * 10000);
}
}
{
ll suma = 0, sumb = 0;
int idx = 0;
ForE(i, 1, n){
sumb += b[i];
while (idx + 1 <= n and suma < sumb){
idx++;
suma += a[idx];
}
ans = max(ans, min(suma, sumb) - (ll)(i + idx) * 10000);
}
}
cout << fixed << setprecision(4) << (ld)ans / 10000 << endl;
}
/*
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INPUT: |
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OUTPUT: |
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*/
