#include<bits/stdc++.h>
#define ll long long
#define db double
using namespace std;
const int N=100005;
db A[N+3],B[N+3];
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int n;
cin>>n;
for(int i=1;i<=n;i++){
cin>>A[i]>>B[i];
}
sort(A+1,A+n+1,greater<db>());
sort(B+1,B+n+1,greater<db>());
db sa=0.0,sb=0.0,ans=0.0;
int pa=1,pb=1;
for(int i=1; i<=2*n; i++){
// CHANGE: Use a very small value to represent an invalid/impossible move
db ca = -1e18, cb = -1e18;
// CHANGE: Correctly calculate the guaranteed profit (min outcome - total bets)
// If we pick from A, the new profit is min(sa + A[pa], sb) - cost i
if(pa <= n) ca = min(sa + A[pa], sb) - i;
// If we pick from B, the new profit is min(sa, sb + B[pb]) - cost i
if(pb <= n) cb = min(sa, sb + B[pb]) - i;
// CHANGE: Added strict bounds checking (pa <= n, pb <= n)
// and fixed the comparison logic to ensure we always pick the better move
if(pa <= n && (ca >= cb)){
sa += A[pa];
pa++;
ans = max(ans, ca);
}
else if(pb <= n){
sb += B[pb];
pb++;
ans = max(ans, cb);
}
}
cout<<fixed<<setprecision(4)<<ans;
return 0;
}
