#include<bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
int n;
double a[N], b[N];
int main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin >> n;
for(int i = 1; i <= n; i++){
cin >> a[i] >> b[i];
a[i] -= 1;
b[i] -= 1;
}
sort(a + 1, a + n + 1);
reverse(a + 1, a + n + 1);
sort(b + 1, b + n + 1);
reverse(b + 1, b + n + 1);
double ans = 0, sum_a = 0, sum_b = 0;
for(int na = 0, nb = 0; na <= n; na++){
if(na){
sum_a += a[na];
}
while(nb + 1 <= n && min(sum_a - nb, sum_b - na) < min(sum_a - (nb + 1), sum_b + a[nb + 1] - na)){
sum_b += b[nb + 1];
nb += 1;
}
//cout << sum_a << " " << sum_b << " " << na << " " << nb << "\n";
ans = max(ans, min(sum_a - nb, sum_b - na));
}
cout << fixed << setprecision(4) << ans;
}
