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

#define ll long long
#define elif else if
#define vi vector<int>
#define vll vector<ll>
#define vvi vector<vi>
#define pii pair<int,int>


#define repname(a, b, c, d, e, ...) e
#define rep(...)                    repname(__VA_ARGS__, rep3, rep2, rep1, rep0)(__VA_ARGS__)
#define rep0(x)                     for (int rep_counter = 0; rep_counter < (x); ++rep_counter)
#define rep1(i, x)                  for (int i = 0; i < (x); ++i)
#define rep2(i, l, r)               for (int i = (l); i < (r); ++i)
#define rep3(i, l, r, c)            for (int i = (l); i < (r); i += (c))





struct ScalarInput {
    template<class T>
    operator T(){
        T ret;
        cin >> ret;
        return ret;
    }
};
struct VectorInput {
    size_t n;
    VectorInput(size_t n): n(n) {}
    template<class T>
    operator vector<T>(){
        vector<T> ret(n);
        for(T &x : ret) cin >> x;
        return ret;
    }
};
ScalarInput input(){ return ScalarInput(); }
VectorInput input(size_t n){ return VectorInput(n); }

template<typename T>
void print(vector<T> a){
  for(int i=0;i<a.size();i++){
    cout<<a[i]<<" \n"[i+1==a.size()];
  }
}

template<class T>
void print(T x){
    cout << x << '\n';
}
 
template <class Head, class... Tail>
void print(Head&& head, Tail&&... tail){
  cout << head << ' ';
  print(forward<Tail>(tail)...);
}

using D=long double;

D calc(D t1,D t2,D p){
  if(t1>t2)swap(t1,t2);
  if(t1+p<t2)return (t1/2.0)+(t1+p/2.0)/2.0;
  else return (t1/2.0)+(t2-(t2-t1)*(t2-t1)/(2.0*p))/2;
}

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout<<fixed<<setprecision(15);

  int h,w;
  D p;
  cin>>h>>w>>p;
  vector<vector<D>>dp(h+1,vector<D>(w+1,1e15));
  dp[h-1][w-1]=0;
  for(int x=h-1;x>=0;x--){
    for(int y=w-1;y>=0;y--){
      if(x==(h-1)&&y==w-1)continue;
      dp[x][y]=calc(dp[x+1][y],dp[x][y+1],p);
    }
  }
  print(dp[0][0]);
}