#include<bits/stdc++.h>
typedef long long ll;
using namespace std;
const int N=510;
const ll mod=1000000007;
const ll inf=1e15;
double a[N],b[N];
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
int n;cin>>n;
vector<double>v;
for (int i=1;i<=n;i++) {
cin>>a[i]>>b[i];
v.push_back(a[i]);
v.push_back(b[i]);
}
sort(a+1,a+n+1);
sort(b+1,b+n+1);
reverse(a+1,a+n+1);
reverse(b+1,b+n+1);
for (int i=2;i<=n;i++) a[i]+=a[i-1];
for (int i=2;i<=n;i++) b[i]+=b[i-1];
double res=0.0;
for (int i=1;i<=n;i++){
for (int j=1;j<=n;j++){
res=max(res,min(a[i]-i-j,b[j]-i-j));
}
}
cout<<setprecision(4)<<fixed<<res<<endl;
return 0;
}
