#include <bits/stdc++.h>
using ll = long long;
using namespace std;
#define int ll
int a[100005], b[100005];
int mx1[100005], mx2[100005];
int32_t main(){
ios_base::sync_with_stdio(false); cin.tie(0);
int n;
cin >> n;
for(int i=1; i<=n; i++){
double x, y;
cin >> x >> y;
a[i]=llround(x*10000);
b[i]=llround(y*10000);
//cout << a[i] << ' ' << b[i] << '\n';
}
sort(a+1, a+n+1, greater<int>());
sort(b+1, b+n+1, greater<int>());
for(int i=1; i<=n; i++){
mx1[i]=mx1[i-1]+a[i];
mx2[i]=mx2[i-1]+b[i];
}
int ans=0;
for(int i=0; i<=n; i++){
int j=lower_bound(mx2, mx2+n+1, mx1[i])-mx2;
if(j>0)ans=max(ans, min(mx1[i], mx2[j-1])-(i+j-1)*10000);
if(j<=n)ans=max(ans, min(mx1[i], mx2[j])-(i+j)*10000);
}
cout << fixed << setprecision(4) << double(ans)/10000;
return 0;
}
/*
4
1.4 3.7
1.2 2
1.6 1.4
1.9 1.5
0.5000
*/
