1 #include <iostream>
2 #include <cstdlib>
3 #include <cstdio>
4 #include <algorithm>
5 #include <vector>
6 #include <queue>
7 #include <cmath>
8 #include <stack>
9 #include <cstring>
10
11 using namespace std;
12
13 #define INF 0xfffffff
14 #define maxn 10005
15
16 int main()
17 {
18 __int64 n, dp[maxn] = {1, 2, 3, 5};
19
20 while(scanf("%I64d", &n) != EOF)
21 {
22 for(int i = 3; i <= n; i++)
23 dp[i] = dp[i-3] + dp[i-1];
24 printf("%I64d\n", dp[n]-1); // 减去一种什么都不放的情况
25
26 }
27 return 0;
28 }