#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
  int A,B;
  cin>>A>>B;
  if(A-B < 0){
      cout<<0<<endl;
      return 0;
  } 
  int ans = 1;
  for(int i=0;i<A-B;i++){
      ans *= 2;
  }
  cout<<ans<<endl;
}