#include <bits/stdc++.h>

using namespace std;

int n, m;
double p;
double f(double t1, double t2, double p) {
  if (t1 < t2) {
    return t1;
  }
  if (t2 + p < t1) {
    return t2 + p / 2;
  }
  return t1 - 0.5 * (t1 - t2) * (t1 - t2) / p;
}

double dp[1010][1010];

int main() {
  scanf("%d%d%lf", &n, &m, &p);
  dp[1][1] = 0;
  for (int i = 2; i <= n; i++) {
    dp[i][1] = dp[i - 1][1] + p / 4;
  }
  for (int i = 2; i <= m; i++) {
    dp[1][i] = dp[1][i - 1] + p / 4;
  }
  for (int i = 2; i <= n; i++) {
    for (int j = 2; j <= m; j++) {
      dp[i][j] = 0.5 * (f(dp[i - 1][j], dp[i][j - 1], p) +
                        f(dp[i][j - 1], dp[i - 1][j], p));
    }
  }
  printf("%.10f\n", dp[n][m]);
}