#include<bits/stdc++.h>
using namespace std;
struct student
{
	int fs[22],maxx=INT_MIN,minn=INT_MAX;
	double pin=0;
}a[111];
int main()
{
	int n,m;
	cin>>n>>m;
    for(int i=1;i<=n;i++) 
		for(int j=1;j<=m;j++) 
			cin>>a[i].fs[j];
    for(int i=1;i<=n;i++) 
    {
		for(int j=1;j<=m;j++) 
		{
			a[i].pin=a[i].pin+a[i].fs[j];
			if(a[i].fs[j]>a[i].maxx)
				a[i].maxx=a[i].fs[j];
			else if(a[i].fs[j]<a[i].minn)
				a[i].minn=a[i].fs[j];
		}
    	a[i].pin=1.0*(a[i].pin-a[i].maxx-a[i].minn)/(m*1.0-2.0)*1.0;
	}
	for(int i=2;i<=n;i++) 
		if(a[i].pin>a[1].pin)
			a[1].pin=a[i].pin;
	printf("%.2f",a[1].pin);
    return 0;
}