#include<stdio.h>
int maxscore(int n,int m,int a[n][m])
{
	int i,j;
	int max=-1,min=9999;
	double score=0;
	double sum[n];
	for(i=0;i<n;i++)
	{
		max=min=a[i][0];
		for(j=0;j<m;j++)
		{
			if(a[i][j]>max)
			{
				max=a[i][j];
			}
			if(a[i][j]<min)
			{
				min=a[i][j];
			}
			sum[i]+=a[i][j];
		}
		sum[i]=sum[i]-max-min;
		sum[i]/=m;
		if(sum[i]>score)
		{
			score=sum[i];
		}
	}
	printf("%.2f",score);
	return 0;
}
int main()
{
	int n,m,i,j;
	scanf("%d %d",&n,&m);
	int a[n][m];
	for(i=0;i<n;i++)
	{
		for(j=0;j<m;j++)
		{
			scanf("%d",&a[i][j]);
		}
	}
	maxscore(n,m,a);
	return 0;
}