#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vii;
typedef pair<int,int> pi;
typedef vector<pi> pii;
typedef tuple<int,int,int> tii;
typedef vector<ll> li;
typedef vector<li> lii;
#define REP(i,a,b) for(int i=a;i<b;i++)
#define F first
#define S second
#define PB push_back
#define MP make_pair
#define LSOne(s) ((s)&(-s))
ll INF=1e18+10;
int inf=1e9+10;
ll M=1e9+7;
int main() {
int n;cin>>n;
vector<double> a(n),b(n);
REP(i,0,n)cin>>a[i]>>b[i];
sort(a.begin(),a.end());
sort(b.begin(),b.end());
reverse(a.begin(),a.end());
reverse(b.begin(),b.end());
double ans=0;
vector<double> c(n),d(n);
c[0]=a[0]-1;
REP(i,1,n)c[i]=a[i]+c[i-1]-1;
d[0]=b[0]-1;
REP(i,1,n)d[i]=b[i]+d[i-1]-1;
REP(i,0,n)REP(j,0,n)ans=max(ans,min(c[i]-j-1,d[j]-i-1));
cout<<fixed<<setprecision(4)<<ans;
}
