// #pragma GCC optimize("O3,Ofast,unroll-loops")
// #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#include <bits/stdc++.h>
using namespace std;
#define ld long double
#define lli long long int
#define MP make_pair
#define pb push_back
#define REP(i,n) for(int i = 0; (i) < (n); (i)++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
void fastio() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
}
const double EPS = 0.00001;
const int INF = 1e9+500;
const int N = 3e5+5;
const int ALPH = 26;
const int LGN = 25;
constexpr int MOD = 1e9+7;
int n,m,q;
vector<ld> a, b;
inline void solve() {
cin>>n;
ld ans = 0;
a.resize(n);
b.resize(n);
REP(i, n) {
cin >> a[i] >> b[i];
}
sort(rall(a));
sort(rall(b));
int i = 0, j = 0;
ld cura = 0, curb = 0;
while(i < n || j < n) {
if(cura < curb) {
if(i >= n) break;
cura += a[i];
i++;
}
else {
if(j >= n) break;
curb += b[j];
j++;
}
ans = max(ans, min(cura, curb) - (i + j));
}
cout << fixed << setprecision(4) << ans << "\n";
}
signed main() {
fastio();
int test = 1;
//cin>>test;
while(test--) {
solve();
}
}
