//order_of_key(k): Number of items strictly smaller than k .
//find_by_order(k): K-th element in a set (counting from zero).
//#pragma GCC optimize("O3,unroll-loops")
//#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#define file(s) if(fopen(s".in","r")) freopen(s".in","r",stdin);freopen(s".out","w",stdout)
#define all(x) (x).begin(), (x).end()
#define len(x) (int)x.size()
#define tm (tl + tr >> 1)
#define ls v << 1, tl, tm
#define rs v << 1 | 1, tm + 1, tr
#define pb push_back
#define pf push_front
#define popb pop_back
#define popf pop_front
#define elif else if
#define F first
#define S second
#define int long long
using namespace std;
using namespace __gnu_pbds;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
typedef unsigned long long ull;
typedef long long ll;
typedef double db;
typedef long double ld;
const int MOD = 1e9 + 7;
const int N = 2e5 + 7;
const int P = 911;
const ll INF = 1e18;
int rnd() {
int x = rand() << 15;
return x ^ rand();
}
db a[N], b[N];
void GazizMadi() {
db ans = 0, p = 0, q = 0;
int n;
cin >> n;
for (int i = 1; i <= n; i++) {
cin >> a[i] >> b[i];
}
sort(a + 1, a + n + 1, greater <db>());
sort(b + 1, b + n + 1, greater <db>());
for (int i = 1, j = 0; i <= n; i++) {
p += a[i] - 1;
q--;
ans = max(ans, min(p, q));
while (q < p) {
q += b[++j] - 1;
p--;
ans = max(ans, min(p, q));
}
}
cout << fixed << setprecision(4);
cout << ans;
}
const bool Cases = 0;
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
srand(time(0));
int TT = 1;
if (Cases) cin >> TT;
for (int i = 1; i <= TT; i++) {
//cout << "Case " << i << ": ";
GazizMadi();
}
}
