/*input
4
1.4 3.7
1.2 2
1.6 1.4
1.9 1.5
*/
#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 int long long
#define double long double
#define f first
#define s second
#define mp make_pair
#define pb push_back
#define RE(i,n) for (int i = 1; i <= n; i++)
#define RED(i,n) for (int i = n; i > 0; i--)
#define REPS(i,n) for(int i = 1; (i*i) <= n; i++)
#define REP(i,n) for (int i = 0; i < (int)n; i++)
#define FOR(i,a,b) for (int i = a; i < b; i++)
#define REPD(i,n) for (int i = n-1; i >= 0; i--)
#define FORD(i,a,b) for (int i = a; i >= b; i--)
#define all(v) v.begin(),v.end()
#define pii pair<int,int>
#define vi vector<int>
#define vvi vector<vi>
#define print(arr) for (auto it = arr.begin(); it != arr.end(); ++it) cout << *it << " "; cout << endl;
#define debug(x) cout << x << endl;
#define debug2(x,y) cout << x << " " << y << endl;
#define debug3(x,y,z) cout << x << " " << y << " " << z << endl;
typedef tree<
int,
null_type,
less<int>,
rb_tree_tag,
tree_order_statistics_node_update>
ordered_set;
const int INF = 1e18+1;
const int MOD = 1e9+7;
const double PI = 3.14159265358979323846264338;
int raise(int a,int n,int m = MOD){
if(n == 0)return 1;
if(n == 1)return a;
int x = 1;
x *= raise(a,n/2,m);
x %= m;
x *= x;
x %= m;
if(n%2)x*= a;
x %= m;
return x;
}
int floor1(int n,int k){
if(n%k == 0 || n >= 0)return n/k;
return (n/k)-1;
}
int ceil1(int n,int k){
return floor1(n+k-1,k);
}
const int N = 1e5+1;
double a[N];
double b[N];
double pref1[N];
double pref2[N];
int n;
bool cmp(double x,double y){
return x > y;
}
void solve(){
cin >> n;
RE(i,n)cin >> a[i] >> b[i];
sort(a+1,a+n+1,cmp);
sort(b+1,b+n+1,cmp);
pref1[0] = pref2[0] = 0;
RE(i,n){
pref1[i] = pref1[i-1]+a[i];
pref2[i] = pref2[i-1]+b[i];
//cout << i << " " << pref1[i] << " " << pref2[i] << endl;
}
double ans = 0;
REP(i,n+1){
double term1 = pref1[i]-i;
double term2 = -(double)i;
int lo = 0;
int hi = n;
if(cmp(term1-lo,term2+pref2[lo]-lo) == cmp(term1-hi,term2+pref2[hi]-hi)){
double op1 = min(term1-lo,term2+pref2[lo]-lo);
double op2 = min(term1-hi,term2+pref2[hi]-hi);
ans = max(ans,max(op1,op2));
continue;
}
bool ini = cmp(term1-lo,term2+pref2[lo]-lo);
while(lo < hi){
int mid = (lo+hi)/2;
bool here = cmp(term1-mid,term2+pref2[mid]-mid);
if(here == ini)lo = mid+1;
else hi = mid;
}
//cout << "WOW " << i << " " << lo << " ";
hi = lo;
lo--;
double op1 = min(term1-lo,term2+pref2[lo]-lo);
double op2 = min(term1-hi,term2+pref2[hi]-hi);
ans = max(ans,max(op1,op2));
//cout << max(op1,op2) << endl;
}
cout << fixed << setprecision(4) << ans;
}
signed main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
//freopen(".in","r",stdin);freopen(".out","w",stdout);
int t = 1;
//cin >> t;
while(t--){
solve();
}
return 0;
}
