#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>

using namespace std;

typedef long long ll;

int power(int v, int u) {
    if (u == 0  ) {
        return 1;
    }
    if (u % 2 == 0){
        return power(v, u / 2) * power(v, u / 2);
    }
    else {
        return v * power(v, u - 1);
    }
}


int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n, k;
    cin >> n >> k;
    vector<int> dp(n + 1);
    if (k == 1) {
        cout << 1 << "\n";
        return 0;
    }
    for (int i = 0; i < k; ++i) {
        dp[i] = power(2, i);
    }
    for (int i = 0; i < k; ++i) {
        dp[k] += dp[i];
    }
    for (int i = k + 1; i <= n; ++i) {
        dp[i] = dp[i - 1] + dp[i - 1] - dp[i - k - 1];
    }
    cout << dp[n] << "\n";
}