n,m=map(int,input().split())
if m>n:
    n,m=m,n
p=float(input())
if n==1 and m==1:
    ans=p
elif n==1:
    ans=2*p**2+(m-2)*p**3
elif n==2 and m==2:
    ans=4*p**3
elif n==2:
    ans=4*p**3+(n*m-4)*p**4
else:
    ans=4*p**3+(2*(n-2)+2*(m-2))*p**4+(n-2)*(m-2)*p**5
print(ans)