//gm --- akezhon
#include <bits/stdc++.h>
// #pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math,O3")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define pb push_back
#define pf push_front
#define F first
#define S second
#define all(v) v.begin(),v.end()
#define pii pair<int,int>
#define tm (tl+tr)/2
#define TL v+v, tl, tm
#define TR v+v+1, tm+1, tr
#define DA l <= tl && tr <= r
#define NE r < tl || tr < l
// #define double long double
#define int long long
using namespace std;
const int N=2e5+7;
const int mod=998244353;
const int inf=2e18;
void AlemAmenov(){
int n;
cin >> n;
vector<double>a, b;
for(int i=1; i <= n; i++){
double x, y;
cin >> x >> y;
a.pb(x);
b.pb(y);
}
a.pb(0);
b.pb(0);
sort(all(a));
sort(all(b));
reverse(a.begin()+1, a.end());
reverse(b.begin()+1, b.end());
for(int i=1; i <= n; i++){
a[i]+=a[i-1];
b[i]+=b[i-1];
}
double ans=0;
for(int i=1; i <= n; i++){
int l=1, r=n;
while(l <= r){
int m1=l+(r-l)/3;
int m2=r-(r-l)/3;
double x = min(a[i]-i-m1, b[m1]-i-m1);
double y = min(a[i]-i-m2, b[m2]-i-m2);
ans = max({ans, x, y});
if(x < y)l=m1+1;
else r=m2-1;
}
}
cout << fixed << setprecision(4) << ans;
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int RealName=1;
// cin >> RealName;
// srand(time(0));
while(RealName--)
AlemAmenov();
return 0;
}
