import sys
import math


n = int(input())
out=0
inside=0
sep=0
counterins=0 # for the avg deep
d=dict() # vertical moy
counterout=0
compteurGLOBAL=0
lineMoy=0

for i in range(n):
    line = input().lower()
    if i==0 or i==n-1:

        for a in line: #might be useless
            out+=ord(a)-96
            counterout+=1

        if i==0: # We prepare the vertical pool line
            for z in range(len(line)-1):
                if z!=0 and z!=len(line):
                    d[z]=line[z]

        else: # We end the vertical pool line
            for z in range(len(line)-1):
                if z!=0 and z!=len(line):
                    d[z]+=line[z]

    else:
        #Initializing vars for lineMoy
        outcounter=0
        outCounterTEMP=0
        inscounter=0
        insCounterTEMP=0
        for a in range(len(line)):
            if a==0 or a==len(line)-1:
                outcounter+=ord(line[a])-96
                outCounterTEMP+=1
            else:
                inscounter+=ord(line[a])-96
                insCounterTEMP+=1
        lineMoy+=(outcounter/outCounterTEMP)-(inscounter/insCounterTEMP)
        compteurGLOBAL+=1
        for z in range(len(line)-1):#vertical Lines
            if z!=0 and z!=len(line):
                d[z]+=line[z]

for i in d:
    outcounter=0
    outCounterTEMP=0
    inscounter=0
    insCounterTEMP=0
    for a in range(len(d[i])):
        if a==0 or a==len(d[i])-1:
            outcounter+=ord(d[i][a])-96
            outCounterTEMP+=1
        else:
            inscounter+=ord(d[i][a])-96
            insCounterTEMP+=1
    lineMoy+=(outcounter/outCounterTEMP)-(inscounter/insCounterTEMP)
    compteurGLOBAL+=1
length,width=n-2,n-2 #this good
print((lineMoy/compteurGLOBAL)*length*width)
"""insid=(inside/counterins)
outsid=(out/counterout)
print(insid,"\n",outsid)
print(length*width*(outsid-insid))"""