很经典的问题，由于递推公式比较诡异，所以特地的记录下来。
1: #include <stdio.h>
2: #define maxn 100
3:
4: unsigned long long f[maxn];
5: int n,m;
6:
7: int main()
8: {
9: f[0]=1;
10: scanf("%d%d",&n,&m);
11: for (int i=1;i<=n;++i)
12: {
13: f[i]=f[i-1]*2;
14: if (i-m-1>=0) f[i]-=f[i-m-1];
15: if (i-m-1==-1) f[i]-=1;
16: }
17: printf("%I64d\n",f[n]);
18: return 0;
19: }
20: