//
//  main.cpp
//  核电站
//
//  Created by Qing Liu on 16/3/29.
//  Copyright © 2016年 Qing Liu. All rights reserved.
//

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cmath>
#define maxn 60
using namespace std;
typedef long long LL;
LL dpp[maxn];
int main() {
    freopen("nucle.in", "r", stdin);
    freopen("nucle.out", "w", stdout);
    int m,n;
    cin>>n>>m;
    dpp[0]=1;
    for (int i=1; i<=m; i++) {
        dpp[i]+=2*dpp[i-1];
    }
    dpp[m]-=1;
    for (int i=m+1; i<=n; i++) {
        dpp[i]=2*dpp[i-1]-dpp[i-m-1];
    }
    cout<<dpp[n];
    return 0;
}