#include <bits/stdc++.h>
#define rep(i,n) for (int i=0; i<(n); ++i)
using namespace std;
using ll=long long;
int main(){
    int n,k;
    cin>>n>>k;
    if(n-k>=0)cout<<pow(2,(n-k))<<endl;
    else cout<<0<<endl;
}