#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    int n, k;
    cin >> n >> k;
    vector<vector<ll>> dp(n, vector<ll>(2));
    dp[k - 1][0] = 1;
    for(int i = 0; i + 1 < n; i++){
        for(int j = i + 1; j < n; j++){
            for(int k = 0; k < 2; k++){
                dp[j][k | (j != i + 1)] += dp[i][k];
            }
        }
    }
    ll ans = 0;
    for(int i = 0; i < n; i++){
        ans += dp[i][1];
        if(k != 1)ans += dp[i][0];
    }
    cout << ans << endl;
}