#include <bits/stdc++.h>
#define fi first
#define se second
#define mp make_pair
#define TASK ""
#define bit(x) (1LL << (x))
#define getbit(x, i) (((x) >> (i)) & 1)
#define ALL(x) (x).begin(), (x).end()
using namespace std;
template <typename T1, typename T2> bool mini(T1 &a, T2 b) {
if (a > b) {a = b; return true;} return false;
}
template <typename T1, typename T2> bool maxi(T1 &a, T2 b) {
if (a < b) {a = b; return true;} return false;
}
mt19937_64 rd(chrono::steady_clock::now().time_since_epoch().count());
int rand(int l, int r) {
return l + rd() % (r - l + 1);
}
const int N = 1e5 + 5;
const int oo = 1e9;
const long long ooo = 1e18;
const int mod = 1e9 + 7; // 998244353;
const long double pi = acos(-1);
const int base = 1e4;
int need[2 * N];
int t[N];
int r[N];
int n;
int fix(string s) {
int pos = 0;
while (pos < (int) s.size() && s[pos] != '.')
pos++;
if (pos == (int) s.size())
s += '.';
int cnt = (int) s.size() - pos - 1;
while (cnt < 4) {
s += '0';
cnt++;
}
// cerr << s << "\n";
int res = 0;
for (char c : s)
if (c != '.')
res = 10 * res + c - '0';
return res;
}
bool solve(long long lim) {
for (int i = 1; i <= 2 * n; i++)
need[i] = 0;
{
long long tot = 0;
for (int x = 1, i = 1; x <= 2 * n; x++) {
while (i <= n && tot - x * base < lim) {
tot += t[i];
i++;
}
// cerr << tot << " " << x << " " << tot - x * base << " " << i << "\n";
if (tot - x * base >= lim)
need[x] += i - 1;
else
need[x] += oo;
}
}
{
long long tot = 0;
for (int x = 1, i = 1; x <= 2 * n; x++) {
while (i <= n && tot - x * base < lim) {
tot += r[i];
i++;
}
if (tot - x * base >= lim)
need[x] += i - 1;
else
need[x] += oo;
}
}
for (int i = 1; i <= 2 * n; i++)
if (need[i] <= i)
return true;
return false;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
#ifdef ONLINE_JUDGE
freopen("sure.inp","r",stdin);
freopen("sure.out","w",stdout);
#endif
cin >> n;
for (int i = 1; i <= n; i++) {
string x,y;
cin >> x >> y;
t[i] = fix(x);
r[i] = fix(y);
cerr << t[i] << " " << r[i] << "\n";
}
sort(t + 1, t + n + 1, greater <int>());
sort(r + 1, r + n + 1, greater <int>());
long long lo = 0;
long long hi = 1e18;
while (hi - lo > 1) {
long long mid = (lo + hi) >> 1;
if (solve(mid))
lo = mid;
else
hi = mid;
}
cout << lo / base << ".";
{
int cnt = to_string(lo % base).size();
while (cnt < 4) {
cout << 0;
cnt++;
}
cout << lo % base;
}
return 0;
}
