#include <bits/stdc++.h>
using namespace std;
int n,pt1,pt2;
long double sum1,sum2,a[100005],b[100005],ans;
int main(){
ios::sync_with_stdio(false);
cin >> n;
for (int i=1;i<=n;i++){
cin >> a[i] >> b[i];
}
sort(a+1,a+1+n); sort(b+1,b+1+n);
reverse(a+1,a+1+n); reverse(b+1,b+1+n);
while (pt1 < n || pt2 < n){
if (pt2 == n || (pt1 < n && sum1 < sum2)){
pt1++;
sum1+=a[pt1];
}
else
{
pt2++;
sum2+=b[pt2];
}
ans=max(ans,min(sum1,sum2)-pt1-pt2);
}
cout << fixed << setprecision(4) << ans << "\n";
return 0;
}
