#include <bits/stdc++.h>
#pragma GCC optimize("O3")
using namespace std;
double f(int x, int y, vector<double>& a, vector<double>& b){
return min(a[x], b[y])-x-y;
}
int main(){
cin.tie(0);
ios::sync_with_stdio(0);
cout << setprecision(4) << fixed;
int n;
double sol = 0;
cin >> n;
vector<double> a(n), b(n);
for(int i = 0; i < n; i++) cin >> a[i] >> b[i];
sort(a.rbegin(), a.rend());
sort(b.rbegin(), b.rend());
a.insert(a.begin(), 0);
b.insert(b.begin(), 0);
for(int i = 1; i <= n; i++) a[i] += a[i-1], b[i] += b[i-1];
for(int i = 0; i <= n; i++){
int l = 0, h = n, m;
while(l < h){
if(l == h-1){
if(f(i, l, a, b) > f(i, h, a, b)) h--;
else l++;
}
else{
m = (l+h)/2;
if(f(i, m, a, b) >= f(i, m+1, a, b)) h = m;
else l = m+1;
}
}
sol = max(sol, f(i, l, a, b));
}
cout << sol << "\n";
}
