#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include<iomanip>
using namespace std;
using ll = long long;

int main()
{
    ll n, k;
    cin >> n >> k;
    if (k > 1) cout << pow(2, n-k) << endl;
    else {
        if (n == 2) cout << 0 << endl;
        else cout << pow(2, n-1-k) + (n-2) << endl;
    }
}