#include <bits/stdc++.h>
using namespace std;
#define REP(i,a) for(int i = 0; i < (a); i++)
#define ALL(a) (a).begin(),(a).end()
typedef long long ll;
typedef pair<int, int> P;
const int INF = 1e9;
const int MOD = 1e9 + 7;

long long mod_pow(long long x, long long n){
    long long res = 1;
    while(n > 0){
        if(n & 1) res = res * x;
        x = x * x;
        n >>= 1;
    }
    return res;
}

signed main(){
    ll n,k;
    cin >> n >> k;
    if(n < k){
        cout << 0 << endl;
    }else{
        cout << mod_pow(2, n - k) << endl;
    }
}