/* -*- coding: utf-8 -*-
 *
 * 926.cc:  No.926 休日の平均 - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_B = 1000;

/* typedef */

/* global variables */

int hs[MAX_B * 2 + 1];

/* subroutines */

/* main */

int main() {
  int a, b, c;
  scanf("%d%d%d", &a, &b, &c);

  for (int i = 0; i < b * 2; i++)
    hs[i + 1] = hs[i] + ((i % b < c) ? 1 : 0);

  int d = a % b;
  int sum = 0;
  for (int i = 0; i < b; i++)
    sum += hs[i + d] - hs[i];

  printf("%.8lf\n", (double)sum / b + a / b * c);
  return 0;
}