#include <bits/stdc++.h>
#define ld long double
using namespace std;
const int N = 100100;
vector<ld> a, b;
ld apref[N], bpref[N];
int n;
ld f(int a, int x) {
return min(bpref[a]-(a+x), apref[x]-(a+x));
}
int bin_search(int x) {
// searching in b, x
int index = 0;
for(int cekor = n; cekor > 0; cekor/=2) {
while(index + cekor <= n && f(index+cekor, x)<f(index+cekor+1, x)) index+=cekor;
}
return index+1;
}
int main() {
cin>>n;
ld x, y;
for(int i=0;i<n;i++) {
cin>>x>>y;
a.push_back(x);
b.push_back(y);
}
sort(a.rbegin(), a.rend());
sort(b.rbegin(), b.rend());
for(int i=1;i<=n;i++) {
apref[i] = apref[i-1] + a[i-1];
bpref[i] = bpref[i-1] + b[i-1];
}
ld result = 0;
for(int i=1;i<=n;i++) {
int x = bin_search(i);
result = max(result, min(apref[i]-(i+x), bpref[x]-(i+x)));
}
cout<<setprecision(4)<<fixed<<result<<"\n";
return 0;
}
