#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
#define fastio ios::sync_with_stdio(false), cin.tie(0)
#define pb push_back
#define eb emplace_back
#define f first
#define s second
#define int long long
const int maxn = 2e5 + 5;
signed main(void){
fastio;
int n;
cin>>n;
vector<double> a(n), b(n);
for(int i = 0; i < n; i++) cin>>a[i]>>b[i];
sort(a.begin(), a.end(), greater<double>());
sort(b.begin(), b.end(), greater<double>());
int id = 0, id2 = 0;
double ta = 0, tb = 0;
double ans = 0;
for(int i = 0; i < 2 * n; i++){
if(id < n && ta <= tb){
ta += a[id++];
}
else if(id2 < n && tb <= ta){
tb += b[id2++];
}
else break;
ans = max(ans, min(ta, tb) - i - 1);
}
cout<<fixed<<setprecision(4)<<ans<<"\n";
}
