//#pragma GCC optimize("Ofast,unroll-loops,no-stack-protector")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <bits/stdc++.h>
using namespace std;
#define debug(s) cout<< #s <<" = "<< s <<endl
#define all(v) (v).begin(), (v).end()
#define KeepUnique(v) (v).erase( unique(all(v)), v.end() )
#define MEMSET(a,val) memset(a, val, sizeof a)
#define PB push_back
#define endl '\n'
typedef long long ll;
inline int myrand(int l, int r) {
int ret = rand(); ret <<= 15; ret ^= rand();
if(ret < 0) ret = -ret; ret %= (r-l+1); ret += l;
return ret;
}
template <typename F, typename S>
ostream& operator << (ostream& os, const pair< F, S>& p) {
return os<<"(" <<p.first<<", "<<p.second<<")"; }
typedef pair<int, int> ii;
template<typename T> using min_pq =
priority_queue<T, vector<T>, greater<T> >;
//int dx[] = {-1, +0, +1, +0};
//int dy[] = {+0, +1, +0, -1};
typedef long long ll;
ll scale = 10000;
ll read() {
string s; cin >> s;
for(char &b : s) if(b == '.') b = ' ';
stringstream is(s);
string x, y;
is >> x; is >> y;
while(y.size() < 4) y += "0";
ll xx, yy;
is = stringstream(x); is >> xx;
is = stringstream(y); is >> yy;
return xx * scale + yy;
}
const int maxn = 100010;
vector<ll> L, R, LR;
int n;
ll solve(int k) {
ll final = 0;
int ret = -1, lo = 0, hi = min(n, k);
while(lo <= hi) {
int mid = lo + hi >> 1;
int rem = min(k - mid, n);
if(L[mid] > R[rem]) {
hi = mid - 1;
} else {
ret = mid;
lo = mid + 1;
}
} assert(ret != -1);
final = L[ret];
ret = -1, lo = 0, hi = min(n, k);
while(lo <= hi) {
int mid = lo + hi >> 1;
int rem = min(k - mid, n);
if(R[mid] > L[rem]) {
hi = mid - 1;
} else {
ret = mid;
lo = mid + 1;
}
} assert(ret != -1);
final = max(final, R[ret]);
return final - scale * k;
// ll ret = -1e18;
// for(int i = 0; i <= min(k, n); i++) {
// ret = max(ret, min(L[i], R[min(n, k - i)]));
// } return ret - k * scale;
}
ll gen(ll i, ll took, ll x, ll y) {
if(i == n) return min(x, y) - took * scale;
ll ret = 0;
ret = max(ret, gen(i + 1, took, x, y));
ret = max(ret, gen(i + 1, took + 1, x + L[i], y));
ret = max(ret, gen(i + 1, took + 1, x, y + R[i]));
ret = max(ret, gen(i + 1, took + 2, x + L[i], y + R[i]));
return ret;
}
int32_t main () {
cout << fixed << setprecision(4);
cin >> n;
L.resize(n), R.resize(n);
for(int i = 0; i < n; i++) {
L[i] = read();
R[i] = read();
//cout << L[i] << ' ' << R[i] << endl;
}
//cout << (double)gen(0, 0, 0, 0) / double(scale) << endl;
sort(all(L)), sort(all(R));
reverse(all(L)), reverse(all(R));
for(int i = 1; i < n; i++) L[i] += L[i - 1], R[i] += R[i - 1];
L.insert(L.begin(), 0); R.insert(R.begin(), 0);
ll mx = -1e18;
for(int i = 0; i <= (n << 1); i++) {
mx = max(mx, solve(i));
} cout << double(mx) / double(scale) << endl;
}
