#include <bits/stdc++.h>
using namespace std;
double A[100005];
double B[100005];
double X[100005];
double Y[100005];
int main(){
int N; cin >> N;
for (int i = 1; i <= N; i++){
cin >> A[i] >> B[i];
}
sort(A, A + N + 1);
sort(B, B + N + 1);
for (int i = 1; i <= N; i++){
X[i] = X[i - 1] + (A[N - i + 1] - 1);
Y[i] = Y[i - 1] + (B[N - i + 1] - 1);
}
double lo = 0;
double hi = 1e9;
for (int x = 0; x <= 70; x++){
double mid = (lo + hi)/2;
bool fnd = false;
for (int i = 1; i <= N; i++){
double y = X[i] - mid;
int k = (int) y;
if (k < 0){
continue;
}
if (k >= N){
k = N;
}
if (Y[k] - i >= mid) fnd = true;
}
if (!fnd) hi = mid;
else{
lo = mid;
}
}
printf("%.4lf", lo);
}
