#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
#define ff first
#define ss second
#define pii pair<int,int>
#define vii vector <int>
#define endl '\n'
#define lb lower_bound
#define ub upper_bound
const int inf = 1e18;
const int N = 2e5+5;
inline void test_case() {
int n;
cin >> n;
double a[n+5],b[n+5];
for (int i = 1; i <= n; i++) {
cin >> a[i] >> b[i];
}
sort(a+1,a+n+1,greater<double>());
sort(b+1,b+n+1,greater<double>());
double ans = 0;
int l = 0;
int r = 0;
double a1 = 0, b1 = 0;
while (true) {
if (l >= n && r >= n) break;
if (l >= n && r < n) {
r++;
b1 += b[r];
} else if (r >= n && l < n) {
l++;
a1 += a[l];
} else if (a1 <= b1) {
l++;
a1 += a[l];
} else {
r++;
b1 += b[r];
}
ans = max(ans,min(a1,b1)-l-r);
}
printf("%.4lf",(double)ans);
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int T = 1;
// cin >> T;
while (T--) test_case();
}
