#include<stdio.h>
int  nyan_int(const void *a, const void *b)
{
    return *(int*)a - *(int*)b;
}

int main(){
	int N;
    int K[55];
	double ans = 0.0;
	scanf("%d", &N);
	for (int a = 0; a < N;a++){
		scanf("%d", &K[a]);
	}
	qsort(K, N, sizeof(int), nyan_int);

	for (int b = 0; b < N - 2;b++){
		K[b + 1] = (K[b + 1] + K[b])/2;
	}
  ans=(K[N-1]+K[N-2])*0.5;
	printf("%f", ans);
	return 0;
}