#include<bits/stdc++.h>
//#include<ext/pb_ds/assoc_container.hpp>
//#include<ext/pb_ds/tree_policy.hpp>
#define el '\n'
#define fi first
#define sc second
//#define int ll
#define pii pair<int, int>
#define all(v) v.begin(), v.end()
using namespace std;
//#define ordered_set tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update>
//using namespace __gnu_pbds;
using ll=long long;
using ull=unsigned long long;
using ld=long double;
const int mod=1e9+7;
const int N=1e5+11;
// find_by_order, order_of_key
int n;
ld a[N], b[N];
void sol()
{
cin >> n;
for(int i=0; i<n; i++)
{
cin >> a[i] >> b[i];
a[i]--;
b[i]--;
}
sort(a, a+n);
sort(b, b+n);
reverse(a, a+n);
reverse(b, b+n);
int id=0;
ld ans1=0, ans2=0, ans=0;
for(int i=0;i<n;i++)
{
ans1 += a[i];
while(id<n && min(ans1-id, ans2-i-1) < min(ans1-id-1, ans2+b[id]-i-1))
{
ans2 += b[id];
id++;
}
ans = max(ans, min(ans1-id, ans2-i-1));
}
cout << fixed << setprecision(4) << ans;
}
signed main()
{
// freopen("SUREBET.INP", "r", stdin);
// freopen("SUREBET.OUT", "w", stdout);
ios_base::sync_with_stdio(0);
cin.tie(0);
int t=1;
//cin >> t;
while(t--)
{
sol();
}
}
