#include <bits/stdc++.h>
#define pb push_back
using namespace std;
#define F first
#define sz size()
#define S second
#define in insert
#define lb lower_bound
#define int long long
#define all(v) v.begin(), v.end()
#define FOR(x, n, m, d) for(int x = n; x <= m; x += d)
#define FORR(x, n, m, d) for(int x = n; x >= m; x -= d)
#define nikita ios_base::sync_with_stdio(0), cin.tie(0);
const int N = 1e5+5;
int n,m,tt,sum=0,l, r, x, y, cnt, block = 448, res;
int a[N], b[N], c[N], dp[N], pref[N];
void solve() {
cin >> n;
double dx, dy, ans = 0, k = 0, sum1 = 0, sum2 = 0, ok = 0;
multiset<double>v, vec;
FOR(i, 1, n, 1){
cin >> dx >> dy;
v.in(dx), vec.in(dy);
}
ans = 0;
int ko = 0;
FOR(i, 1, 2*n, 1){
if(sum1 >= sum2){
if(!vec.sz)break;
ok = *vec.rbegin();
sum2 += ok;
vec.erase(vec.find(*vec.rbegin()));
}
else{
if(!v.sz)break;
ok = *v.rbegin();
sum1 += ok;
v.erase(v.find(*v.rbegin()));
}
ko ++;
k = min(sum1, sum2);
ans = max(ans, k - ko);
}
printf("%.4lf",(double)ans);
}
signed main()
{
nikita
tt = 1;
if(!tt)cin >> tt;
FOR(i, 1, tt, 1){
solve();
}
}
