#include <bits/stdc++.h>
using namespace std;
int main(){
ios::sync_with_stdio(false);
cin.tie(NULL);
int n;
cin>>n;
vector<double>a(n),b(n);
for(int i=0;i<n;i++)cin>>a[i]>>b[i];
sort(a.begin(),a.end(),greater<double>());
sort(b.begin(),b.end(),greater<double>());
vector<double>A(n+1,0),B(n+1,0);
for(int i=1;i<=n;i++){
A[i]=A[i-1]+a[i-1];
B[i]=B[i-1]+b[i-1];
}
double r=0;
for(int i=0;i<=n;i++){
int j1 = int(lower_bound(B.begin(), B.end(), A[i]) - B.begin());
for(int dj=-1; dj<=0; dj++){
int j = j1 + dj;
if(j<0||j>n) continue;
double p = min(A[i], B[j]) - (i + j);
if(p>r) r=p;
}
}
if(r<0) r=0;
cout<<fixed<<setprecision(4)<<r<<"\n";
return 0;
}
