#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef double db;

const int N = 1047;
const db INF = 1e18;
db dp[N][N];

db get(int i, int j)
{
	if (i < 0 || j < 0)
		return INF;
	return dp[i][j];
}

db p;

db f(db a, db b)
{
	if (a > b)
		swap(a, b);
	if (a + p < b)
		return a + p / 4;
	return a / 2 + b / 2 - (b - a) * (b - a) / (4 * p);
}

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	
	int n, m;
	cin >> n >> m;
	cin >> p;
	dp[0][0] = 0;
	FOR (i, 0, n + 1)
	{
		FOR (j, 0, m + 1)
		{
			if (i == 0 && j == 0) continue;
			dp[i][j] = f(get(i - 1, j), get(i, j - 1));
			
			///cerr << i << ' ' << j << ' ' << dp[i][j] << '\n';
		}
	}
	cout << fixed << setprecision(15) << dp[n - 1][m - 1] << '\n';
	
	return 0;
}