#include <iostream>
#include <iomanip>

int main(void){
  using namespace std;
  long n,k,s=0;

  cin >> n >> k;
  //cout << n << " " << k;

  for(long i=1;i<n+1;i++){
    s += i*k;
  }
  
  //cout << s << " " << n << " " << k << endl;
  cout << fixed << setprecision(4) << (double)s / (double) (n+1) / (double) k << endl;  
  return 0;    
}