#include <bits/stdc++.h>
#define int long long
#define ff first
#define ss second
#define all(x) x.begin(),x.end()
#define pb push_back
using namespace std;
const int N=1e5+5;
signed main(){
int n;
cin>>n;
vector <long double> a(n),b(n);
for(int i=0;i<n;i++){
cin>>a[i]>>b[i];
}
sort(all(a));sort(all(b));
for(int i=n-2;i>=0;i--){
a[i]+=a[i+1];
b[i]+=b[i+1];
}
a.pb(0);
b.pb(0);
long double ans=-1e9;
for(int i=n;i>=0;i--){
for(int j=n;j>=0;j--){
long double sum1=a[i],sum2=b[j];
long double cnt1=n-i,cnt2=n-j;
long double x=min(sum1-cnt1-cnt2,sum2-cnt1-cnt2);
ans=max(ans,x);
}
}
if(ans<0)ans=0;
cout<<fixed<<setprecision(4)<<ans<<"\n";
}
/*
4
1.4 3.7
1.2 2
1.6 1.4
1.9 1.5
*/
