#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define pb push_back
#define sz size
#define mp make_pair
#define ios ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define all(a) a.begin(),a.end()
const int N=1e6+1;
const ll inf=1e18+1;
int n,k=0,mx=0,o=0;
ld v[N*2],d[N*2];
ld bin(int x)
{
int l=0,m,r=x;
while(l+1<r)
{
m=(l+r)>>1;
if(v[m]>=d[x-m])
{
r=m;
}
else
{
l=m;
}
}
return (max(v[r-1],d[x-r])-x);
}
int main()
{
ios
cin>>n;
ld a[n],b[n],ans=0;;
for(int i=0;i<n;++i)
{
cin>>a[i]>>b[i];
}
sort(a,a+n);sort(b,b+n);
v[0]=d[0]=0;
for(int i=0;i<=n*2;++i)
{
v[i+1]=v[i];
d[i+1]=d[i];
if(i<n)
{
v[i+1]+=a[n-i-1];
d[i+1]+=b[n-1-i];
}
}
for(int i=0;i<=n*2;++i)
{
ans=max(ans,bin(i));
}
cout<<fixed<<setprecision(4)<<ans;
}
