AC

#include <stdio.h>
#include <algorithm>

int a[61];

int main(){
    int n;
    scanf("%d",&n);
    for (int i=0;i<n;i++) scanf("%d",&a[i]);
    std::sort(a,a+n);
    for (int i=0;i<n;i+=2) printf("%d ",a[i]);
    for (int i=n-2;i>=1;i-=2) printf("%d ",a[i]);
    return 0;
}