#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
#include <string>
#include <assert.h>
#include <map>
using namespace std;
typedef long long int ll;
typedef vector <ll> vi;
typedef vector <vi> vvi;
typedef vector <double> vd;
int main (){
cout.setf(ios::fixed);
cout.precision(4);
int n;
cin >> n;
vd A(n), B(n);
for (int i = 0; i < n; ++i){
cin >> A[i] >> B[i];
}
sort(A.rbegin(), A.rend());
sort(B.rbegin(), B.rend());
double pa = 0, pb = 0;
int ia = 0, ib = 0;
double solution = 0;
while (ia < n and ib < n){
if (pa >= pb) {
pa -= 1;
pb += (B[ib] - 1);
++ib;
}
else {
pb -= 1;
pa += (A[ia] - 1);
++ia;
}
solution = max(solution, min(pa, pb));
}
cout << solution << endl;
}
