#include <bits/stdc++.h>
using namespace std;
const int N=2e5+10;
const double eps=1e-4; 
int n;
double a[N],b[N]; 
int main() {
	freopen("wager.in","r",stdin);
	freopen("wager.out","w",stdout); 
	scanf("%d",&n);
	for (int i=1;i<=n;i++) scanf("%lf%lf",&a[i],&b[i]);
	sort(a+1,a+n+1),sort(b+1,b+n+1);
	int l=n,r=n;
	double x=0,y=0,ans=0;
	for (int i=1;i<=2*n;i++)
	{
//		if (i<=n) cout<<a[i]<<" "<<b[i]<<endl; 
		if (l&&x-y<-eps) x+=a[l],l--;
		else if (r&&x-y>eps) y+=b[r],r--;
		else
		{
//			cout<<"qwq "<<i<<endl; 
			if (l&&a[l]-b[r]>eps) x+=a[l],l--;
			else y+=b[r],r--;
		}
		ans=max(ans,min(x,y)-1.0*i);
	}
	printf("%.4f",ans); 
}