//apig's property
//Happiness can be found, even in the darkest of times, if one only remembers to turn on the light
//El Pueblo Unido Jamas Sera Vencido
//Do or do not... there is no try
//Billions of bilious blue blistering barnacles in a thundering typhoon!
#include<bits/stdc++.h>
#define fast ios_base::sync_with_stdio(0) , cin.tie(0) , cout.tie(0)
#define F first
#define S second
#define pb push_back
#define vll vector< ll >
#define vi vector< int >
#define pll pair< ll , ll >
#define pi pair< int , int >
#define all(s) s.begin() , s.end()
#define sz(s) s.size()
#define str string
#define md ((s + e) / 2)
#define mid ((l + r) / 2)
#define msdp(dp) memset(dp , -1 , sizeof dp)
#define mscl(dp) memset(dp , 0 , sizeof dp)
#define C continue
#define R return
#define B break
#define lx node * 2
#define rx node * 2 + 1
#define br(o) o ; break
#define co(o) o ; continue
using namespace std;
typedef long long ll;
ll q, dp[100005], k, l, m, n, o, p;
map < ll , ll > mp;
vll adj[555555];
const ll mod = 1e9+7;
str s;
double a[555555] , b[555555] ;
void solve(){
cin >> n ;
for(ll i = 1 ; i <= n ; i++){
cin >> a[i] >> b[i] ;
}
sort(a + 1 , a + n + 1 , greater < double > ()) ;
sort(b + 1 , b + n + 1 , greater < double > ()) ;
ll i = 0 , j = 0 ;
double ans = 0 , suma = 0 , sumb = 0 ;
while(i < n && j < n){
if(suma < sumb){
suma += a[++i] ;
}
else {
sumb += b[++j] ;
}
ans = max(ans , min(suma - i - j , sumb - i - j)) ;
}
while(i < n){
suma += a[++i] ;
ans = max(ans , min(suma - i - j , sumb - i - j)) ;
}
while(j < n){
sumb += b[++j] ;
ans = max(ans , min(suma - i - j , sumb - i - j)) ;
}
cout << fixed << setprecision(4) << ans << endl ;
}
int main(){
fast ;
q = 1 ;
//cin >> q ;
while(q--){
solve() ;
}
}
