// Author : hejinming2012
#include <bits/stdc++.h>
#define int long long
#define endl '\n'
#define dbg(x) cout << #x " = " << (x) << endl
#define quickio ios::sync_with_stdio(false);
#define quickin cin.tie(0);
#define quickout cout.tie(0);

using namespace std;
inline int read() {
    int now = 0, nev = 1; char c = getchar();
    while(c < '0' || c > '9') { if(c == '-') nev = -1; c = getchar(); }
    while(c >= '0' && c <= '9') { now = (now << 1) + (now << 3) + (c & 15); c = getchar(); }
    return now * nev;
}
void write(int x) {
    if(x < 0) putchar('-'), x = -x;
    if(x > 9) write(x / 10);
    putchar(x % 10 + '0');
}

signed main() {
    quickio
    quickin
    quickout
    int r, c, p;
    cin >> r >> c >> p;
    vector < vector <double> > dp;
    dp.resize(r, vector <double> (c));
    for(int i = r - 1; i >= 0; i--)
        for(int j = c - 1; j >= 0; j--)
            if(i == r - 1 && j == c - 1) dp[i][j] = 0;
            else if(i == r - 1) dp[i][j] = 0.25 * p + dp[i][j + 1];
            else if(j == c - 1) dp[i][j] = 0.25 * p + dp[i + 1][j];
            else {
                double a = dp[i + 1][j];
                double b = dp[i][j + 1];
                if(a > b) swap(a, b);
                if(a + p <= b) dp[i][j] = 0.25 * p + a;
                else dp[i][j] = 0.5 * (a + p - b) / p * b + 0.5 * a + 0.5 * (b - a) / p * 0.5 * (a + b);
            }
    cout << fixed << setprecision(10) << dp[0][0] << endl;
    return 0;
}