#include <bits/stdc++.h>
using namespace std;
#define int long long
#define f first
#define s second
using ld = long double;
ld a[100001], b[100001];
signed main(){
int n;
cin >> n;
for (int i = 1;i<=n;++i){
cin >> a[i] >> b[i];
}
ld res = 0;
ld l = 0, r = 1e9;
sort(a+1, a+n+1);
sort(b+1, b+n+1);
while(abs(l-r) >= 1e-6){
ld mid = (l+r)/2.0;
ld s1 = 0, s2 = 0;
int t1 = n, t2 = n;
while(s1 < mid or s2 < mid){
bool check = false;
while(s1 < mid and t1 >= 1){
s1 += a[t1]-1.0;
check = true;
s2 -= 1.0;
t1--;
}
while(s2 < mid and t2>= 1){
s2 += b[t2]-1.0;
s1 -= 1.0;
check = true;
t2--;
}
if(!check)break;
}
if(s1 >= mid and s2>=mid){
res = mid;
l = mid;
}else r = mid;
}
cout << fixed << setprecision(4) << res;
}
