// #ifdef __AVX2__
// #pragma GCC target "avx2"
// #endif
// #pragma GCC optimize "O3"
// #pragma GCC optimize "unroll-loops"
#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
// using namespace __gnu_pbds;
using namespace std;
#define int long long
#define elif else if
#define all(l) begin(l),end(l)
#define rall(l) rbegin(l),rend(l)
#define append push_back
#define print(l) for(auto i:l) cout<<i<<' '; cout<<endl;
#define pprint(a,b) cout<<a<<' '<<b<<endl;
#define inp(l) for(auto &i:l) cin>>i;
// #define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define pai make_pair
#define endl "\n"
#define pii pair<int,int>
#define fi first
#define se second
#define vec vector
// const int mod=998244353;
const int mod1=998244353;
const int mod=1e9+7;
const int N=2e5+5;
#define pff pair<float,float>
int ind(vec<float>&a,float &x){
int l=0,r=a.size();
while(l!=r){
int m=(l+r)/2;
if(a[m]>=x) r=m;
else l=m+1;
}
return l;
}
int iter=1,itera=1;
void solve(){
int n;
cin>>n;
vec<float>a(n),b(n);
for(int i=0;i<n;i++) cin>>a[i]>>b[i];
sort(rall(a));
sort(rall(b));
vec<float>pa(n+1,0),pb(n+1,0);
for(int i=1;i<=n;i++){
pa[i]=pa[i-1]+a[i-1];
pb[i]=pb[i-1]+b[i-1];
}
float ans=0,eps=5e-5;
for(int i=0;i<=2*n;i++){
float l=0,r=1e9+1e-5;
while(l+eps<r){
float m=(l+r)/2;
if(pa[n]<m or pb[n]<m) r=m-eps;
else{
if(ind(pa,m)+ind(pb,m)<=i) l=m;
else r=m-eps;
}
}
ans=max(ans,l-i);
}
printf("%.4lf",(double)ans);
}
signed main(){
// freopen("","r",stdin);
// freopen("","w",stdout);
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
// cout<<fixed<<setprecision(20);
// cin>>itera;
// cout<<endl;
for(iter=1;iter<=itera;iter++) solve();
}
