#include <bits/stdc++.h>
#define file(s) if (fopen(s".in", "r")) freopen(s".in", "r", stdin), freopen(s".out", "w", stdout)
#define optimus_prime ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define fxd(x) fixed << setprecision(x)
#define all(a) (a.begin() , a.end())
#define popcount(x) __builtin_popcount(x)
#define lwb lower_bound
#define upb upper_bound
#define dl long double
#define ll long long
#define pb push_back
#define sz() size()
#define F first
#define S second
using namespace std;
const ll N = 2e5+9;
ll n;
dl a[N] , b[N] , zr=0;
dl calc(ll cnt){
ll ind1=1 , ind2=1 , i=cnt;
dl sum1=0 , sum2=0;
while (cnt){
cnt--;
if (ind1>n){
sum2+=b[ind2];
ind2++;
continue;
}
if (ind2>n){
sum1+=a[ind1];
ind1++;
continue;
}
if (sum1<sum2)sum1+=a[ind1++];
else if (sum1>sum2)sum2+=b[ind2++];
else {
if (a[ind1]>b[ind2])sum1+=a[ind1++];
else sum2+=(b[ind2++]);
}
}
sum1-=i;
sum2-=i;
return min(sum1 , sum2);
}
void solve(){
cin >> n;
for (int i = 1 ; i <= n ; i++)cin >> a[i] >> b[i];
sort (a+1 , a+1+n);
sort (b+1 , b+1+n);
reverse (a+1 , a+1+n);
reverse (b+1 , b+1+n);
dl ans=0;
for (int i = 1 ; i <= n*2 ; i++)ans=max(ans , calc(i));
cout << fxd(4) << ans;
}
signed main() {
optimus_prime;
solve();
return 0;
}
