#!/usr/bin/python2
# -*- coding: utf-8 -*-
# †
from decimal import *

def f(N, M, p):
    if N > M:
        N, M = M, N
    s = [0] * 5
    if N == 1:
        if M > 1:
            s[1] = 2
            s[2] = M-2
    else:
        s[2] = 4
        s[3] = 2 * (N-2 + M-2)
        s[4] = (N-2) * (M-2)
    res = N*M * p
    for i in [1, 2, 3, 4]:
        res -= s[i] * (1-p**i) * p
    return res


N, M = map(int, raw_input().split())
p = Decimal(raw_input())
res = f(N, M, p)
print '{:.10f}'.format(res)