#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
using P = pair<int,int>;

int main(void){
    ll n, k;
    cin >> n >> k;
    if(n - k >= 0){
        cout << pow(2LL, n - k) << endl;
    }
    else{
        cout << 0 << endl;
    }
    return 0;
}