#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
const int N=1e5+10;
int n,a[N],b[N],mk[N];
double ans=0.0,u[N],v[N];
bool cmp(double a,double b){
	return a>b;
}
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",u+i,v+i);	
	sort(u+1,u+1+n,cmp);
	sort(v+1,v+1+n,cmp);
	for(int i=1;i<=n;i++)u[i]+=u[i-1];
	for(int i=1;i<=n;i++)v[i]+=v[i-1];
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			ans=max(ans,min(u[i],v[j])-1.0*(i+j));
		}
	}
	printf("%.4lf\n",ans);
	return 0;
}