#include <bits/stdc++.h>
#define int long long
using namespace std;
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(NULL);
int n;
cin >> n;
double a[n+1], b[n+1];
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>());
double prefA[n+1] = {0}, prefB[n+1] = {0};
prefA[1] = a[1];
prefB[1] = b[1];
for (int i = 2; i <= n; i++){
prefA[i] = prefA[i-1] + a[i];
prefB[i] = prefB[i-1] + b[i];
}
double ans = 0;
for (int i = 1; i <= n; i++){
int l = 1, r = n;
while (l <= r){
ans = max(ans, min(prefA[i] - (double)i - (double)l, prefB[l] - (double)i - (double)l));
l++;
}
}
cout << fixed << setprecision(4) << ans;
}
