#include <bits/stdc++.h>
using namespace std;
#define FOR(i, j, k) for(int i=(j); i<=(k); i++)
#define FFOR(i, j, k) for(int i=(j); i<(k); i++)
#define DFOR(i, j, k) for(int i=(j); i>=(k); i--)
#define bug(x) cerr<<#x<<" = "<<(x)<<'\n'
#define pb push_back
#define mp make_pair
#define bit(s, i) (((s)>>(i))&1LL)
#define mask(i) ((1LL<<(i)))
#define builtin_popcount __builtin_popcountll
#define __builtin_popcount __builtin_popcountll
using ll=long long; using ld=long double;
mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count()); const ld pi=acos(0)*2;
template <typename T> inline void read(T &x){char c; bool nega=0; while((!isdigit(c=getchar()))&&(c!='-')); if(c=='-'){nega=1; c=getchar();} x=c-48; while(isdigit(c=getchar())) x=x*10+c-48; if(nega) x=-x;}
template <typename T> inline void writep(T x){if(x>9) writep(x/10); putchar(x%10+48);}
template <typename T> inline void write(T x){if(x<0){ putchar('-'); x=-x;} writep(x);}
template <typename T> inline void writeln(T x){write(x); putchar('\n');}
#define taskname "Bet"
int n;
vector <ld> a;
vector <ld> b;
int main(){
#ifdef Aria
if(fopen(taskname".in", "r"))
freopen(taskname".in", "r", stdin);
#endif // Aria
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin>>n;
a.resize(n);
b.resize(n);
FFOR(i, 0, n) cin>>a[i]>>b[i];
sort(a.begin(), a.end());
sort(b.begin(), b.end());
ld ans=0;
ld suma=0, sumb=0;
FOR(bet, 1, n*2){
if(suma<sumb){
if(a.empty()) break;
suma+=a.back();
a.pop_back();
}
else{
if(b.empty()) break;
sumb+=b.back();
b.pop_back();
}
ans=max(ans, min(suma, sumb)-bet);
}
cout<<setprecision(4)<<fixed<<ans;
}
