// cre: Nguyen Ngoc Hung - Train VOI 2024
#include<bits/stdc++.h>
using namespace std;
#define __nnhzzz__ signed main()
#define BIT(i,j) ((i>>j)&1LL)
#define MASK(i) (1LL<<i)
#define ALL(x) (x).begin(),(x).end()
#define SZ(x) (int)(x).size()
#define fi first
#define se second
#define ll long long
#define ull unsigned long long
#define ld long double
#define vi vector<int>
#define vvi vector<vi>
#define vvvi vector<vvi>
#define pii pair<int,int>
#define vpii vector<pii>
#define REP(i,a,b) for(int i = (a); i<=(b); ++i)
#define REPD(i,a,b) for(int i = (a); i>=(b); --i)
#define REPDIS(i,a,b,c) for(int i = (a); i<=(b); i+=c)
//-------------------------------------------------------------//
const int oo = 1e9,LOG = 20,MAXN = 1e5+7,N = 2e3+3;
const int MOD = 1e9+7,MOD1 = 1e9+207,MOD2 = 1e9+407,MOD3 = 998244353;
//-------------------------------------------------------------//
template<typename T1, typename T2> bool mini(T1 &a, T2 b){if(a>b){a=b;return true;}return false;}
template<typename T1, typename T2> bool maxi(T1 &a, T2 b){if(a<b){a=b;return true;}return false;}
/*
----------------------------------------------------------------
END OF TEMPLATE
----------------------------------------------------------------
Nguyen Ngoc Hung - nnhzzz
Training for VOI24 gold medal
----------------------------------------------------------------
*/
ld a[MAXN],b[MAXN],prea[MAXN],preb[MAXN];
void solve(){
int n; cin >> n;
REP(i,1,n) cin >> a[i] >> b[i];
sort(a+1,a+n+1); reverse(a+1,a+n+1);
sort(b+1,b+n+1); reverse(b+1,b+n+1);
REP(i,1,n){
prea[i] = prea[i-1]+a[i];
preb[i] = preb[i-1]+b[i];
}
ld res = 0;
REP(i,1,n){
int pos = lower_bound(preb+1,preb+n+1,prea[i])-preb;
if(pos!=n+1) maxi(res,prea[i]-i-pos);
pos = lower_bound(prea+1,prea+n+1,preb[i])-prea;
if(pos!=n+1) maxi(res,preb[i]-i-pos);
}
cout << fixed << setprecision(4) << res;
}
__nnhzzz__{
ios::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
#define name "test"
if(fopen(name".inp","r")){
freopen(name".inp","r",stdin);
freopen(name".out","w",stdout);
}
#define name1 "nnhzzz"
if(fopen(name1".inp","r")){
freopen(name1".inp","r",stdin);
freopen(name1".out","w",stdout);
}
int test = 1;
while(test--){
solve();
}
cerr << "\nTime elapsed: " << 1000*clock()/CLOCKS_PER_SEC << "ms\n";
return 0;
}
