#include "bits/stdc++.h"
using namespace std;
#ifdef N_N_C
#include "debug.h"
#else
#define cebug(...) "Arya"
#endif
#define int long long
const int N=1e5+5;
const int mod=1e9+7;
int n;
double a[N],b[N],p1[N],p2[N];
void sol(){
cin>>n;
for(int i=1; i<=n; i++) cin>>a[i]>>b[i];
sort(a+1,a+n+1);
sort(b+1,b+n+1);
reverse(a+1,a+n+1);
reverse(b+1,b+n+1);
for(int i=1; i<=n; i++) p1[i]=p1[i-1]+a[i];
for(int i=1; i<=n; i++) p2[i]=p2[i-1]+b[i];
auto f2 = [&](double x) -> int{
int l=1,r=n,ans=-1;
while(l<=r){
int mid=(l+r)>>1;
if(p2[mid]-x>=0.0){
ans=mid;
r=mid-1;
}else l=mid+1;
}
return ans;
};
auto f1 = [&](double x) -> int{
int l=1,r=n,ans=-1;
while(l<=r){
int mid=(l+r)>>1;
if(p1[mid]-x>=0.0){
ans=mid;
r=mid-1;
}else l=mid+1;
}
return ans;
};
double ans=0;
for(int i=1; i<=n; i++){
int j=f2(p1[i]);
if(j==-1) continue;
ans=max(ans,p1[i]-i-j);
}
for(int i=1; i<=n; i++){
int j=f1(p2[i]);
if(j==-1) continue;
ans=max(ans,p2[i]-i-j);
}
cout<<fixed<<setprecision(4)<<ans;
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
// freopen(".inp", "r", stdin);
// freopen(".out", "w", stdout);
int tt=1;
//cin>>tt;
while(tt--){
sol();
}
cerr << "\nTime elapsed: " << 1000.0 * clock() / CLOCKS_PER_SEC << " ms.\n";
return 0;
}
