#include <bits/stdc++.h>
using namespace std;
const int N=1e5+5;
int n,l; double res,sum,sumTwo;
double a[N],b[N];
int main()
{
ios_base::sync_with_stdio(NULL);
cin.tie(NULL); cout.tie(NULL);
cin >> n;
for (int i=1;i<=n;i++)
cin >> a[i] >> b[i];
sort(a+1,a+n+1,greater<double>());
sort(b+1,b+n+1,greater<double>());
sum=sumTwo=0;
l=1;
for (int i=1;i<=n;i++)
{
sumTwo+=b[i];
res=max(res,min(sum,sumTwo)-i-l+1);
while (l<=n and sum<=sumTwo)
{
sum+=a[l];
l++;
res=max(res,min(sum,sumTwo)-i-l+1);
}
}
cout << setprecision(4) << fixed << res;
}
