#include <iostream>
#include <string>
#include <cmath>

using namespace std;

int main(){
  int num,num2;
  long long int ans;
  cin>>num>>num2;
  if(num<num2){
    ans=0;
    cout<<0<<endl;
  }else{
    ans=pow(2,num-num2);
    cout<<ans<<endl;
  }
}