#include <bits/stdc++.h>
#define ll long long
#define pb push_back
using namespace std;
const int mod = 1e9+7;
const ll inf = 1e18;
const int N = 2e5+5;
int n;
double a[N], b[N];
double best = 0;
void gen(vector<int>&v) {
if(v.size() == n) {
double ans1 = 0, ans2 = 0;
for(int i = 0;i<n;i++) {
if(v[i] == 0) continue;
if(v[i] == 1) {
ans1+=a[i]-1.0;
}
if(v[i] == 2) {
ans1-=1.0;
}
if(v[i] == 3) {
ans1+= a[i]-2.0;
}
}
for(int i = 0;i<n;i++) {
if(v[i] == 0) continue;
if(v[i] == 1) {
ans2-=1.0;
}
if(v[i] == 2) {
ans2+=b[i]-1.0;
}
if(v[i] == 3) {
ans2+= b[i]-2.0;
}
}
best = max(best, min(ans1,ans2));
return;
}
for(int i = 0;i<=3;i++) {
v.pb(i);
gen(v);
v.pop_back();
}
}
void solve() {
cin >> n;
for(int i = 0;i<n;i++) {
cin >> a[i] >> b[i];
}
vector<int>v;
gen(v);
cout << fixed << setprecision(4) << best;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int tt=1;
//cin >> tt;
while(tt--) {
solve();
}
//
return 0;
}
