#include <bits/stdc++.h>
using namespace std;

#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define all(x) begin(x), end(x)
#define sz(x) int((x).size())
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;

#ifdef LOCAL
auto operator<<(auto& o, auto x) -> decltype(x.first, o);
auto operator<<(auto& o, auto x) -> decltype(x.end(), o) {
  o << "{";
  for (int i = 0; auto y : x) o << ", " + !i++ * 2 << y;
  return o << "}";
}
auto operator<<(auto& o, auto x) -> decltype(x.first, o) {
  return o << "(" << x.first << ", " << x.second << ")";
}
void __print(auto... x) { ((cerr << x << " "), ...) << endl; }
#define debug(x...) __print("[" #x "]:", x)
#else
#define debug(...) 2137
#endif

using db = double;


int main() {
  cin.tie(0)->sync_with_stdio(0);

  int n, m;
  cin >> n >> m;
  db p;
  cin >> p;
  --n;
  --m;
  vector dp(n + 1, vector(m + 1, db(0)));

  auto calka = [&](db a, db b) {
    if(b < a)
      return b * p;
    db odl = min(b - a, p);
    return (a + a + odl) * odl / 2 + (p - odl) * b;
  };
  const db inf = 1e18;
  for(int i = 0; i <= n; i++) {
    for(int j = 0; j <= m; j++) {
      if(!i && !j)
        continue;
      db a = i ? dp[i - 1][j] : inf;
      db b = j ? dp[i][j - 1] : inf;
      db c0 = calka(a, b);
      db c1 = calka(b, a);
      db ans = (c0 + c1) / 2 / p;
      debug(c0, c1);
      debug(i, j, a, b, ans);
      dp[i][j] = ans;
    }
  }
  cout << setprecision(9) << fixed << dp[n][m] << endl;
}


/*
[c0, c1]: 0 32 
[i, j, a, b, ans]: 0 1 1e+18 0 2 
[c0, c1]: 16 48 
[i, j, a, b, ans]: 0 2 1e+18 2 4 
[c0, c1]: 32 64 
[i, j, a, b, ans]: 0 3 1e+18 4 6 
[c0, c1]: 32 0 
[i, j, a, b, ans]: 1 0 0 1e+18 2 
[c0, c1]: 16 16 
[i, j, a, b, ans]: 1 1 2 2 2 
[c0, c1]: 16 30 
[i, j, a, b, ans]: 1 2 4 2 2.875 
[c0, c1]: 23 43.1172 
[i, j, a, b, ans]: 1 3 6 2.875 4.13232 
[c0, c1]: 48 16 
[i, j, a, b, ans]: 2 0 2 1e+18 4 
[c0, c1]: 30 16 
[i, j, a, b, ans]: 2 1 2 4 2.875 
[c0, c1]: 23 23 
[i, j, a, b, ans]: 2 2 2.875 2.875 2.875 
[c0, c1]: 23 32.2682 
[i, j, a, b, ans]: 2 3 4.13232 2.875 3.45426 
3.454260103

w
w

*/