#include<bits/stdc++.h>
using namespace std ;
const int maxn = 1e5 + 5 ;
int n ;
double x[maxn], y[maxn], p_x[maxn], p_y[maxn] ;
bool cmp(double a, double b){ return a > b ; }
int main(){
cin >> n ;
for(int i = 1 ; i <= n ; i++) cin >> x[i] >> y[i] ;
sort(x + 1, x + 1 + n, cmp) ; sort(y + 1, y + 1 + n, cmp) ;
for(int i = 1 ; i <= n ; i++) p_x[i] = p_x[i-1] + x[i], p_y[i] = p_y[i-1] + y[i] ;
double ans = 0 ;
for(int i = 1 ; i <= n ; i++){
int ini = 1, fim = n, mid, best = 0 ; double mn = p_x[i] ;
while(ini <= fim){
mid = (ini + fim)>>1 ;
if(abs((p_x[i])-(p_y[mid])) <= mn){
mn = abs((p_x[i])-(p_y[mid])) ;
best = mid ;
}
if(p_x[i] <= p_y[mid]) fim = mid - 1 ;
else ini = mid + 1 ;
}
if(best) ans = max(ans, min(p_x[i] - (double)best - (double)i, p_y[best] - (double)i - (double)best)) ;
}
cout << fixed << setprecision(4) << ans << "\n" ;
}
