#include <bits/stdc++.h>
using namespace std;
#define rep(i, l, r) for (int i = (l); i < (r); ++i)
#define per(i, l, r) for (int i = (r - 1); i >= l; --i)
#define ALL(x) (x).begin(), (x).end()
using i64 = long long;
i64 parse() {
i64 ret = 0;
string s;
cin >> s;
if (find(ALL(s), '.') == s.end()) s.push_back('.');
while (s.end() - find(ALL(s), '.') <= 4) s += '0';
for (const auto e : s) {
if (std::isdigit(e)) {
ret = 10 * ret + (e - '0');
} else {
continue;
}
}
return ret;
}
void out(i64 v) {
cout << v / 10000 << '.';
i64 m = v % 10000;
string s = to_string(m);
while (s.size() < 4) s += '0';
cout << s;
cout << endl;
}
void main_() {
int N;
cin >> N;
vector<i64> A(N), B(N);
rep(i, 0, N) {
A[i] = parse();
B[i] = parse();
}
sort(ALL(A), greater());
sort(ALL(B), greater());
vector<i64> C(N + 1);
rep(i, 0, N) C[i + 1] = C[i] + B[i];
i64 sum = 0;
constexpr i64 X = 10000;
i64 ans = 0;
rep(i, 0, N + 1) {
auto eval = [&](int j) {
i64 a = sum - (i + j) * X;
i64 b = C[j] - (i + j) * X;
return min(a, b);
};
int ok = -1, ng = N;
while (ng - ok > 1) {
const auto m = (ok + ng) / 2;
i64 x = eval(m), y = eval(m + 1);
if (x < y) ok = m;
else ng = m;
}
ans = max(ans, eval(ok + 1));
if (i == N) break;
sum += A[i];
}
out(ans);
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
main_();
}
