#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
#define scan(x) do{while((x=getchar())<'0'); for(x-='0'; '0'<=(_=getchar()); x=(x<<3)+(x<<1)+_-'0');}while(0)
char _;
#define complete_unique(a) a.erase(unique(a.begin(),a.end()),a.end())
#define all(a) a.begin(),a.end()
#define println printf("\n");
#define readln(x) getline(cin,x);
#define pb push_back
#define endl "\n"
#define INT_INF 0x3f3f3f3f
#define LL_INF 0x3f3f3f3f3f3f3f3f
#define MOD 1000000007
#define mp make_pair
#define fastio cin.tie(0); cin.sync_with_stdio(0);
#define MAXN 100005
typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
typedef unordered_map<int,int> umii;
typedef pair<int,int> pii;
typedef pair<double,double> pdd;
typedef pair<ll,ll> pll;
typedef pair<int,pii> triple;
typedef int8_t byte;
mt19937 g1(time(0));
int randint(int a, int b){return uniform_int_distribution<int>(a, b)(g1);}
ll randlong(ll a,ll b){return uniform_int_distribution<long long>(a, b)(g1);}
ll gcd(ll a, ll b){return b == 0 ? a : gcd(b, a % b);}
ll lcm(ll a, ll b){return a*b/gcd(a,b);}
ll fpow(ll b, ll exp, ll mod){if(exp == 0) return 1;ll t = fpow(b,exp/2,mod);if(exp&1) return t*t%mod*b%mod;return t*t%mod;}
ll divmod(ll i, ll j, ll mod){i%=mod,j%=mod;return i*fpow(j,mod-2,mod)%mod;}
int len;
double A[MAXN],B[MAXN],rr;
int main(){
scanf("%d",&len);
for(int i=1; i<=len; i++)
scanf(" %lf %lf",&A[i],&B[i]);
sort(A+1,A+len+1,greater<double>());
sort(B+1,B+len+1,greater<double>());
for(int i=1; i<=len; i++){
A[i]+=A[i-1];
B[i]+=B[i-1];
}
for(int i=1; i<=len; i++){
int low = 1, high = len, ans = 1;
double res = min(A[i]-1-i,B[1]-1-i);
while(low <= high){
int mid = (low+high)/2;
double f = A[i]-mid-i;
double s = B[mid]-mid-i;
if(min(f,s) >= min(A[i]-(mid-1)-i,B[mid-1]-(mid-1)-i)){
ans = mid, res = min(f,s);
low = mid+1;
}else high = mid-1;
}
rr = max(rr,res);
}
printf("%.4f\n",rr);
}
