use std::io::Write;
use std::collections::*;

type Map<K, V> = BTreeMap<K, V>;
type Set<T> = BTreeSet<T>;
type Deque<T> = VecDeque<T>;

// 積分がいるな
//
// 右を示すところに飛び込んだ時
// inf_{0}^{p} L.min(x+D) dx
//

fn main() {
    input! {
        h: usize,
        w: usize,
        p: f64,
    }
    let eval = |base: f64, test: f64| -> f64 {
        let diff = base - test;
        if diff <= 0.0 {
            return base;
        }
        ((p - diff) * base + test * diff + diff * diff * 0.5) / p
    };
    let mut dp = vec![vec![0f64; w]; h];
    for i in (0..h).rev() {
        for j in (0..w).rev() {
            if (i, j) == (h - 1, w - 1) {
                continue;
            }
            let mut val = std::f64::MAX;
            if j + 1 == w {
                val = p * 0.25 + dp[i + 1][j];
            } else if i + 1 == h {
                val = p * 0.25 + dp[i][j + 1];
            } else {
                let r = eval(dp[i][j + 1], dp[i + 1][j]);
                let d = eval(dp[i + 1][j], dp[i][j + 1]);
                val = (r + d) * 0.5;
            }
            dp[i][j] = val;
        }
    }
    println!("{}", dp[0][0]);
}

// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[macro_export]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[macro_export]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[macro_export]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------