x=-1
y=0
b=[]
stop=0
k=int(raw_input())
while k!=stop :
    y+=1
    yy=0
    
    a=[]
    while yy!=y:
        x+=2
        yy+=1
        a.append(x)
    b.append(a)
    #print(b)
    if len(b)==k:
        stop=k
element=b[k-1]
print sum(element)