#include <iostream>
using namespace std;

double sum(int x,int n) {
 float s=0;
 if (n==1) 
	 return 1.0*x/2;
 else {
  s = (sum(x,n-1)+1) * x/2;
  return s;
 }
}
int main() {
 int x,n;
 double a;
 cin>>x>>n;
 a = sum(x,n);
 cout<<a;
 return 0;
}