#include <bits/stdc++.h>
//#include "grader.h"
#define respagold ios_base::sync_with_stdio(0), cin.tie(0);
#define int long long
#define ll long long
#define int2 __int128_t
#define FOR( i, x, n, d ) for( int i = x; i <= n; i += d )
#define FORR( i, x, n, d ) for( int i = x; i >= n; i -= d )
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x.size())
#define pb push_back
#define ins insert
#define lb lower_bound
#define ub upper_bound
#define pii pair <int, int>
#define mkp make_pair
using namespace std;
const int N1 = 2e5 + 123;
int a[N1], b[N1], c[N1], n, m, k, z, w, x, y, dp[N1];
vector <pii> v;
mt19937 rng( chrono::steady_clock::now().time_since_epoch().count());
int rand( int l, int r )
{
uniform_int_distribution <int> uid( l, r );
return uid( rng );
}
double d1[N1], d2[N1], ans, cur, cur2;
void solve()
{
cin >> n;
FOR( i, 1, n, 1 )
{
cin >> d1[i] >> d2[i];
}
sort( d1 + 1, d1 + n + 1 );
sort( d2 + 1, d2 + n + 1 );
reverse( d1 + 1, d1 + n + 1 );
reverse( d2 + 1, d2 + n + 1 );
double l = 0.0, r = n * 1000;
while( r - l >= 0.0001 )
{
double md = (l + r) / 2, suma = 0, sumb = 0;
int le = 0, ri = 0;
while( le <= n && ri <= n && min( suma, sumb ) < md )
{
if( suma < md && le < n ) le ++, suma += d1[le] - 1.0000, sumb --;
if( sumb < md && ri < n ) ri ++, sumb += d2[ri] - 1.0000, suma --;
if( ( le == n && suma < md ) || ( ri == n && sumb < md ) ) break;
}
if( min(suma, sumb) < md ) r = md - 0.00001;
else l = md + 0.00001, ans = md;
}
cout.precision(4);
cout << fixed << ans;
}
signed main()
{
// freopen("connect.in", "r", stdin);
// freopen("connect.out", "w", stdout);
respagold
int test = 1;
if( !test ) cin >> test;
while( test -- )
{
solve();
}
}
// solved by KluydQ
