#include<bits/stdc++.h>
using namespace std;
double a[100005],b[100005];
int main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
int n;
cin >> n;
for(int i=1;i<=n;i++){
cin >> a[i] >> b[i];
a[i]-=1.0;b[i]-=1.0;
}
sort(a+1,a+n+1);
reverse(a+1,a+n+1);
sort(b+1,b+n+1);
reverse(b+1,b+n+1);
for(int i=1;i<=n;i++){
a[i]+=a[i-1];
b[i]+=b[i-1];
}
double ans=-1e9;
for(int i=1;i<=n;i++){
for(int j=1;j<=n;j++)ans=max(ans,min(a[i]-(double)j,b[j]-(double)i));
}
cout << fixed << setprecision(4) << ans << '\n';
return 0;
}
