#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


using Double = long double;

constexpr Double INF = 1e+20;

int M, N;
Double P;
Double dp[1010][1010];

int main() {
  for (; ~scanf("%d%d%Lf", &M, &N, &P); ) {
    for (int x = 0; x < M; ++x) for (int y = 0; y < N; ++y) if (x || y) {
      Double a = x ? dp[x - 1][y] : INF;
      Double b = y ? dp[x][y - 1] : INF;
      if (a > b) {
        swap(a, b);
      }
      // a  or  min{a+x, b} (0 <= x <= P)
      Double &c = dp[x][y] = 0.0L;
      c += a;
      if (a + P <= b) {
        c += a + P / 2.0L;
      } else {
        c += ((b - a) * ((a + b) / 2.0L) + (P - (b - a)) * b) / P;
      }
      c /= 2.0L;
    }
    printf("%.12Lf\n", dp[M - 1][N - 1]);
  }
  return 0;
}