#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), '.') <= 6) s += '0';
for (const auto e : s) {
if (std::isdigit(e)) {
ret = 10 * ret + (e - '0');
} else {
continue;
}
}
return ret;
}
void out(i64 v) {
i64 x = v % 100;
v /= 100;
if (x >= 50) ++v;
cout << v / 10000 << '.';
i64 m = v % 10000;
string s = to_string(m);
while (s.size() < 4) s = '0' + s;
cout << s;
cout << endl;
}
void main_2() {
int N;
cin >> N;
vector<double> A(N), B(N);
rep(i, 0, N) cin >> A[i] >> B[i];
sort(ALL(A), greater());
sort(ALL(B), greater());
long double sumA = 0, sumB = 0;
int i = 0, j = 0;
long double ans = 0;
while (i < N or j < N) {
if (sumA < sumB) {
if (i == N) break;
sumA += A[i];
++i;
} else {
if (j == N) break;
sumB += B[j];
++j;
}
ans = max(ans, min(sumA, sumB) - (long double)(i + j));
}
cout << fixed << setprecision(4) << ans << 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());
i64 sumA = 0, sumB = 0;
int i = 0, j = 0;
i64 ans = 0;
while (i < N or j < N) {
if (sumA < sumB) {
if (i == N) break;
sumA += A[i];
++i;
} else {
if (j == N) break;
sumB += B[j];
++j;
}
ans = max(ans, min(sumA, sumB) - (i + j) * 1000000ll);
}
out(ans);
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
main_();
}
