#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define ld long double
#define ull unsigned long long
#define ff first
#define ss second
#define pii pair<int,int>
#define pll pair<long long, long long>
#define vi vector<int>
#define vl vector<long long>
#define pb push_back
#define rep(i, b) for(int i = 0; i < (b); ++i)
#define rep2(i,a,b) for(int i = a; i <= (b); ++i)
#define rep3(i,a,b,c) for(int i = a; i <= (b); i+=c)
#define count_bits(x) __builtin_popcountll((x))
#define all(x) (x).begin(),(x).end()
#define siz(x) (int)(x).size()
#define forall(it,x) for(auto& it:(x))
using namespace __gnu_pbds;
using namespace std;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
//mt19937 mt;void random_start(){mt.seed(chrono::time_point_cast<chrono::milliseconds>(chrono::high_resolution_clock::now()).time_since_epoch().count());}
//ll los(ll a, ll b) {return a + (mt() % (b-a+1));}
const int INF = 1e9+50;
const ll INF_L = 1e18+40;
const ll MOD = 1e9+7;
int main()
{
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
//random_start();
int n;
cin >> n;
vector<ld> p1,p2;
rep(i,n)
{
ld x,y;
cin >> x >> y;
x--;
y--;
p1.pb(x);
p2.pb(y);
}
sort(all(p1));
reverse(all(p1));
sort(all(p2));
reverse(all(p2));
ld ans = 0;
ld sum1 = 0;
ld sum2 = 0;
int ptr1 = 0;
int ptr2 = 0;
while(ptr1 < n || ptr2 < n)
{
if((ptr1 == n || sum2 < sum1) && ptr2 != n)
{
sum1--;
sum2 += p2[ptr2++];
}
else
{
sum2--;
sum1 += p1[ptr1++];
}
ans = max(ans,min(sum1,sum2));
}
cout << fixed << setprecision(4) << ans;
}
