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


signed main() {
  int N, K;
  cin >> N >> K;
  
  if( N < K ) cout << 0 << endl;
  else{
    N -= K;
    int ans = 1;
    for( int i = 0; i < N; i++ ) ans *= 2;
    cout << ans << endl;
  }
    
}