#!/usr/bin/python2
# -*- coding: utf-8 -*-
# †
from decimal import Decimal
from fractions import Fraction as frac

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


def conv(fra):
    a, b = fra.numerator, fra.denominator
    integer, rem = divmod(a, b)
    v = []
    while True:
        if rem == 0:
            break
        rem *= 10
        quo, rem = divmod(rem, b)
        v.append(quo)
    res = '{}.{}'.format(integer, ''.join(map(str, v)))
    res = res.rstrip('0')
    if res.endswith('.'):
        res = res[:-1]
    return res


N, M = map(int, raw_input().split())
p = frac(Decimal(raw_input()))
res = f(N, M, p)
print conv(res)