#include<bits/stdc++.h>
#define int long long
using namespace std;
int to_number(string s)
{
bool ok = 0;
for(char i : s) if(i == '.') ok = 1;
if(ok == 0) s += ".";
while(s.size() < 5 || s[s.size()-5] != '.') s += "0";
for(int i = 0; i < s.size(); i++) if(s[i] == '.'){
s.erase(s.begin()+i); break;
}
int num = 0;
for(char i : s) num = num * 10 + i - '0';
return num;
}
string num_to_string(int num)
{
string ans = to_string(num);
while(ans.size() < 5) ans = "0" + ans;
ans.insert(ans.end()-4, '.');
return ans;
}
signed main()
{
int n; cin>>n;
vector<int> a, b;
for(int i = 1; i <= n; i++){
string x, y; cin>>x>>y;
a.push_back(to_number(x)); b.push_back(to_number(y));
}
sort(a.begin(), a.end()); sort(b.begin(), b.end());
int ans = 0, x = 0, y = 0;
if(a.back() > b.back()) swap(a, b);
for(int i = 1; i <= 2*n; i++){
if(x < y && a.size() > 0){
x += a.back(); a.pop_back();
}
else{
y += b.back(); b.pop_back();
}
ans = max(ans, min(x, y) - i*10000);
}
cout<<num_to_string(ans);
}
