#include <bits/stdc++.h>
using namespace std;
#define ll long long

ll n;
double a[110000],b[110000];
double ans,a1,a2;
bool vis[110000][4];

bool cmp(double xx,double yy){
	return xx>yy;
}

int main(){
	freopen("wager.in","r",stdin);
	freopen("wager.out","w",stdout);
	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	cin>>n;
	for (int i=1;i<=n;i++){
		cin>>a[i]>>b[i];
	}
	sort(a+1,a+n+1,cmp);
	sort(b+1,b+n+1,cmp);
	ll i=1,j=1;
	while (i<=n&&j<=n){
		if (!vis[i][1]){
			vis[i][1]=1;
			a1+=a[i];
		}
		if (!vis[j][2]){
			a2+=b[j];
			vis[j][2]=1;
		}
		ans=max(ans,min(a1-i-j,a2-i-j));
		if (a1<a2) i++;
		else j++;
	}
	cout<<fixed<<setprecision(4)<<ans;
	return 0;
}