#include <bits/stdc++.h>
using namespace std;
#define Tupizm ios_base :: sync_with_stdio(0), cin.tie(0), cout.tie(0);
#define ONE exit(0);
#define nl "\n"
#define all(x) x.begin(0), x.end(0);
#define sz(x) (int)x.size();
#define pb push_back
#define ppb pop_back
typedef long long ll;
typedef double db;
const int N = 1e5 + 5;
const int M = 1e9 + 7;
int n;
double a[N], b[N];
double ans;
double c[N], d[N];
int main(){
Tupizm
cin >> n;
for(int i = 1; i <= n; ++i){
cin >> a[i] >> b[i];
}
sort(a + 1, a + n + 1);
sort(b + 1, b + n + 1);
for(int i = n; i >= 1; --i){
c[i] = c[i + 1] + a[i];
d[i] = d[i + 1] + b[i];
}
reverse(c + 1, c + n + 1);
reverse(d + 1, d + n + 1);
for(int i = 1; i <= n; ++i){
}
for(int i = 0; i <= n; ++i){
for(int j = 0; j <= n; ++j){
ans = max(ans, (double)(min(c[i], d[j]) - (i + j)));
}
}
cout << fixed << setprecision(4) << (db)ans << nl;
ONE
}
