#include <bits/stdc++.h>
using namespace std;
const int N = 1005;

int n, m;
double dp[N][N], p;

int main() {
    scanf("%d%d%lf", &n, &m, &p);
    for (int i = n; i >= 1; --i)
        for (int j = m; j >= 1; --j) {
            if (i == n && j == m) continue;
            else if (i == n) dp[i][j] = dp[i][j + 1] + p / 4;
            else if (j == m) dp[i][j] = dp[i + 1][j] + p / 4;
            else {
                double x = dp[i + 1][j], y = dp[i][j + 1];
                if (x > y) swap(x, y);
                if (x + p <= y) dp[i][j] = x + p / 4;
                else {
                    double delt = y - x;
                    dp[i][j] = (delt + p) / (2.0 * p) * x + delt * delt / (4.0 * p) + (p - delt) / (2.0 * p) * y;
                }
            }
        }
    printf("%.10lf\n", dp[1][1]);
    return 0;
}