#include <bits/stdc++.h>

using namespace std;

const int N = 1005;

double f[N][N];

signed main() {
    int n, m, p; scanf("%d%d%d", &n, &m, &p);
    for (int i = n; i >= 1; --i) {
        for (int j = m; j >= 1; --j) {
            if (i == n && j == m) {
                f[i][j] = 0;
            } else if (i == n) {
                f[i][j] = f[i][j + 1] + (p / 4.0);
            } else if (j == m) {
                f[i][j] = f[i + 1][j] + (p / 4.0);
            } else {
                double mn = min(f[i + 1][j], f[i][j + 1]),
                       del = abs(f[i + 1][j] - f[i][j + 1]);
                f[i][j] = mn / 2 + (mn + (min(del, (double)p) / 2) * (min(del, (double)p) / p) + del * (1 - min(del, (double)p) / p)) / 2;
            }
        }
    }
    printf("%.10lf\n", f[1][1]);
    return 0;
}