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

signed main(){
  
  int n, m, d;
  
  cin>>n>>m>>d;
  
  double ans = 2.0 * ( n - d ) * ( m - 1 ) / ( n * n );
  
  if( d == 0 ) ans /= 2.0;
  
  printf("%.8f\n", ans);
  
  return 0;
}
