///Never gonna give you up.
#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
typedef long long ll;
using namespace std;
using namespace __gnu_pbds;
template<class x>
using ordered_set = tree<x, null_type,less<x>, rb_tree_tag,tree_order_statistics_node_update>;
const ll mod=(ll)1e9+7;
const ll mod1=998244353;
///the defines :)
#define endl '\n'
#define vi vector<int>
#define vll vector<ll>
#define ent(arr) for(int i=0;i<arr.size();i++)cin>>arr[i];
#define all(arr) arr.begin(),arr.end()
#define allr(arr) arr.rbegin(),arr.rend()
#define sz size()
#define int long long
void preprocess() {}
void solve()
{
int n;
cin>>n;
vector<double> arr1(n);
vector<double> arr2(n);
for(int i=0; i<n; i++)
cin>>arr1[i]>>arr2[i];
sort(allr(arr2));
sort(allr(arr1));
double ansa=0.0,ansb=0.0,ans=0.0;
int j=0;
for(int i=0; i<n; i++)
{
ansa+=(arr1[i]-1.0);
ansb-=1.0;
while(j<n&&(ansa>=ansb))
{
// cout<<ansa<<" "<<ansb<<endl;
ans=max(ans,min(ansa,ansb));
ansb+=arr2[j]-1.0;
ansa-=1.0;
j++;
}
// cout<<ansa<<" "<<ansb<<endl;
ans=max(ans,min(ansa,ansb));
}
cout<<fixed<<setprecision(4)<<ans<<endl;
}
signed main()
{
// freopen("div7.in","r",stdin);
//freopen("div7.out","w",stdout);
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
preprocess();
//bla();
int t=1;
//cin>>t;
while(t--)
solve();
}
