#include<algorithm>
#include<cstdio>
using namespace std;
#define MAX_N 250000

int n, i, t1, t2;
int *heap;

int main(){
    scanf("%d", &n);
    heap = new int[n/2+2];
    for(i = 0; i < n/2+1; ++i){
        scanf("%d", heap+i);
        push_heap(heap, heap+i+1);
    }

    for(i = 0; i < n/2-(n+1)%2; ++i){
        scanf("%d", heap+n/2+1);
        push_heap(heap, heap+n/2+2);
        pop_heap(heap, heap+n/2+2);
    }

    if(n%2){
        printf("%d.0\n", heap[0]);
    }else{
        t1 = heap[0];
        pop_heap(heap, heap+n/2+1);
        t2 = heap[0];
        if((t1+t2)%2){
            printf("%d.5\n", t1/2+t2/2);
        }else{
            printf("%d.0\n", t1/2+t2/2+t1%2);
        }
    }
    delete[] heap;

    return 0;
}