#include<bits/stdc++.h>
using namespace std;
#define V vector
#define pb push_back
#define fi first
#define se second
#define all0(x) (x).begin(), (x).end()
#define all1(x) (x).begin() + 1, (x).end()

typedef pair<int, int> pi;
typedef long long LL;
typedef double db;

const int INF = 2e9 + 10;
const LL INFLL = 8e18 + 10;


void solve() {
    int n, m; cin >> n >> m;
    V<V<db>> dp(n + 2, V<db>(m + 2, INFLL / 2));
    int p; cin >> p;
    // p++;
    for(int i = n; i >= 1; i--) {
        for(int j = m; j >= 1; j--) {
            dp[i][j] = 0;
            if(i == n && j == m) {
                continue;
            }
            //right
            db dis = dp[i + 1][j] - dp[i][j + 1];
            // cout << dis << endl;
            dis = min(dis, (db)p);
            dis = max(dis, (db)0);
            //1 .. dis
            //dis + 1 .. p
            dp[i][j] += (dis * dis / 2 + dp[i][j + 1] * dis + dp[i + 1][j] * (p - dis)) / 2 / p;
            //down
            // cout << "dp" << dp[i][j] << endl;
            {
            db dis = dp[i][j + 1] - dp[i + 1][j];
            dis = min(dis, (db)p);
            dis = max(dis, .0);
            //1 .. dis
            //dis + 1 .. p
            dp[i][j] += (dis * dis / 2 + dp[i + 1][j] * dis + dp[i][j + 1] * (p - dis)) / 2 / p;
            }
        }
    }
    cout << fixed << setprecision(10) << dp[1][1] << endl;
}

int main() {
    solve();
}