#include <bits/stdc++.h>
using namespace std;
#define int long long
// 逆向 大胆 图形
void solve()
{
}
double dp[1005][1005];
signed main(void)
{
    ios::sync_with_stdio(0), cin.tie(0);
    int r, c, p;
    cin >> r >> c >> p;
    for (int i = 1; i <= r; i++) {
        for (int j = 1; j <= c; j++) {
            if (i == 1 && j == 1) {
                dp[i][j] = 0;
            } else if (i == 1) {
                dp[i][j] = 0.25 * p + dp[i][j - 1];
            } else if (j == 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);
                // a < b
                if (a + p <= b) {
                    dp[i][j] = a + 0.25 * p;
                } else {
                    dp[i][j] = 0.5 * a + 0.5 * (p - (b - a)) / p * b + 0.5 * (b - a) / p * (a + (b - a) * 0.5);
                }
            }
        }
    }
    cout << fixed << setprecision(8) << dp[r][c] << '\n';
}