#include<bits/stdc++.h>
#define rc(x) return cout<<x<<endl,0
#define pb push_back
#define mkp make_pair
#define in insert
#define er erase
#define fd find
#define fr first
#define sc second
typedef long long ll;
typedef long double ld;
const int mod=1e9+7;
using namespace std;
int n;
double a[100005], b[100005];
double sum_a[100005], sum_b[100005];
int main(){
cin >> n;
for(int i = 1; i <= n ; i++){
cin >> a[i] >> b[i];
}
sort(a+1,a+n+1);
sort(b+1,b+n+1);
reverse(a+1,a+n+1);
reverse(b+1,b+n+1);
for(int i = 1; i <= n; i++){
sum_a[i] = sum_a[i-1] + a[i];
sum_b[i] = sum_b[i-1] + b[i];
}
double answer = 0;
for(int i = 1; i <= n ; i++){
int l = 1, r = n;
while(l < r){
int mid = (l+r)/2;
if(sum_b[mid] >= sum_a[i]){
r = mid;
}else{
l = mid + 1;
}
}
//cout << i << ' ' << l << '\n';
answer = max(answer,
min(sum_a[i]-i-l,sum_b[l]-i-l));
answer = max(answer,
min(sum_a[i]-i-l+1,sum_b[l-1]-i-l+1));
}
printf("%.4lf",(double)answer);
}
