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#include <bits/stdc++.h>
using namespace std;
int n;
double prvi[1010];
double drugi[1010];
int main(){
cin >> n;
for(int i = 0; i < n; i++){
cin >> prvi[i];
cin >> drugi[i];
}
sort(prvi, prvi+n);
sort(drugi,drugi+n);
double suma_prva = 0;
double suma_druga = 0;
double ans = 0;
for(int i = n-1; i>=0; i--){
suma_prva = suma_prva + prvi[i];
suma_druga = 0;
for(int j = n-1; j>=0; j--){
double broj_prvih = n-i;
double broj_drugih = n-j;
double ukupan = broj_prvih + broj_drugih;
suma_druga = suma_druga + drugi[j];
double rezultat = min(suma_prva - ukupan, suma_druga - ukupan);
ans = max(ans, rezultat);
}
}
printf("%.4lf",(double)ans);
}
