#include <bits/stdc++.h>
#define pb push_back
#define eb emplace_back
#define sz(V) ((int)(V).size())
#define allv(V) ((V).begin()),((V).end())
#define befv(V) ((V)[(sz(V)-2)])
#define sorv(V) sort(allv(V))
#define revv(V) reverse(allv(V))
#define univ(V) (V).erase(unique(allv(V)),(V).end())
#define clv(V) (V).clear()
#define upmin(a,b) (a)=min((a),(b))
#define upmax(a,b) (a)=max((a),(b))
#define rb(x) ((x)&(-(x)))
#define INF (0x3f3f3f3f)
#define INFLL (0x3f3f3f3f3f3f3f3fll)
using namespace std;
typedef long long ll;
typedef long double ld;
const ld EPS = 1e-9;
const int MAXN = 100005;
ll A[MAXN], B[MAXN];
ll Ans;
int N;
ll f(int a, int b) {
return min(A[a], B[b]);
}
ll getAns(int X) {
int s = max(1, X-N), e = min(N, X-1);
for(int m; s < e;) {
m = (s+e)/2;
ll t1 = f(m, X-m), t2 = f(m+1, X-m-1);
if(t1 < t2) s = m+1;
else e = m;
}
return f(s, X-s);
}
int main() {
ios::sync_with_stdio(false);
cin >> N;
for(int i = 1; i <= N; i++) {
ld a, b; cin >> a >> b;
A[i] = a*10000 + EPS;
B[i] = b*10000 + EPS;
}
sort(A+1, A+N+1); reverse(A+1, A+N+1);
sort(B+1, B+N+1); reverse(B+1, B+N+1);
for(int i = 1; i <= N; i++) {
A[i] += A[i-1];
B[i] += B[i-1];
}
for(int i = 2; i <= N*2; i++)
upmax(Ans, getAns(i) - ll(i)*10000);
printf("%.4Lf\n", ld(Ans)/10000 + EPS);
return 0;
}
