#include <bits/stdc++.h>
#define ll long long
#define pb push_back
#define int long long
using namespace std;
const int mod = 1e9+7;
const ll inf = 1e18;
const int N = 2e5+5;
const double eps = 1e-7;
void solve() {
int n;
cin >> n;
vector<double>a(n+1),b(n+1);
for(int i = 1;i<=n;i++) {
cin >> a[i] >> b[i];
}
sort(a.begin()+1,a.end(),greater<double>());
sort(b.begin()+1,b.end(),greater<double>());
vector<double>pr1(n+1), pr2(n+1);
for(int i = 1;i<=n;i++) {
pr1[i] = pr1[i-1]+a[i];
pr2[i] = pr2[i-1]+b[i];
}
double best = -inf;
for(int i = 0;i<=n;i++) {
int l = 0,r = n;
while(r-l>3) {
int m1 = l+(r-l)/3;
int m2 = r-(r-l)/3;
if(min(pr1[i],pr2[m1])-i-m1<min(pr1[i],pr2[m2])-i-m2) {
l = m1;
} else {
r = m2;
}
}
for(int j = l;j<=r;j++) {
best = max(best, min(pr1[i],pr2[j])-i-j);
}
}
cout<<fixed << setprecision(4) << best;
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int tt=1;
//cin >> tt;
while(tt--) {
solve();
}
return 0;
}
