#include <bits/stdc++.h>
using namespace std;
int main(){
ios::sync_with_stdio(false); cin.tie(NULL);
int n; cin >> n;
vector<double> as, bs;
for( int i = 1; i <= n; i++ ){
double a, b; cin >> a >> b;
as.push_back(a);
bs.push_back(b);
}
sort( as.begin(), as.end() );
sort( bs.begin(), bs.end() );
double resp = 0, sa = 0, sb = 0;
for( int i = 1; i <= n; i++ ){
if( sa > sb ){
sb += bs.back();
bs.pop_back();
}
else{
sa += as.back();
as.pop_back();
}
resp = max( resp, min( sa, sb ) - (double)i );
}
cout << fixed << setprecision(4) << resp << endl;
}
