#include <bits/stdc++.h>
using namespace std;
#define N 1010

typedef double db;

db f[N][N];
int n, m; db p;
db Int(db l, db r) {return 1.0 * r * r / 2.0 - 1.0 * l * l / 2.0;}
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);

    cin >> n >> m >> p;
    for (int i = 0; i < n; i ++)
    {
        for (int j = 0; j < m; j ++)
        {
            if (i == 0 && j == 0) continue;
            if (i == 0) {f[i][j] = f[i][j - 1] + p / 4.0; continue;}
            if (j == 0) {f[i][j] = f[i - 1][j] + p / 4.0; continue;}
            
            db x = f[i - 1][j], y = f[i][j - 1];
            if (x > y) swap(x, y);
            f[i][j] += x / 2.0;
            if(y - x <= p) f[i][j] += (Int(x, y) + y * (p - (y - x))) / 2.0 / p;
            else f[i][j] += (Int(x, x + p) / 2.0 / p);
        }
    }


    cout << fixed << setprecision(10) << f[n - 1][m - 1] << '\n'; 
}