#include <iostream>
#include <vector>
#include <cmath>
#include <iomanip>
using namespace std;
#define int long long
const int N=1001;
long long p3[N];
signed main()
{
cout<<fixed<<setprecision(4);
int n;
cin>>n;
p3[0]=1;
for(int i=1;i<=n;i++)
p3[i]=(p3[i-1]*3ll);
vector<double> a,b;
for(int i=0;i<n;i++)
{
double x,y;
cin>>x>>y;
a.push_back(x);
b.push_back(y);
}
double ans=0;
for(long long mask=0;mask<p3[n];mask++)
{
double s1=0,s2=0;
double p=(double)n;
long long cur=mask;
for(int j=0;j<n;j++)
{
if(cur%3==2)
s1+=a[j];
else if(cur%3)
s2+=b[j];
else
p--;
cur/=3;
}
ans=max(ans,min(s1,s2)-p);
}
cout<<ans<<endl;
return 0;
}
