1 /*
2 递推DP: dp[i] 表示放i的方案数,最后累加前n-2的数字的方案数
3 */
4 #include <cstdio>
5 #include <algorithm>
6 #include <cmath>
7 #include <cstring>
8 using namespace std;
9
10 const int MAXN = 1e4 + 10;
11 const int INF = 0x3f3f3f3f;
12 int dp[60];
13
14 int main(void) //URAL 1260 Nudnik Photographer
15 {
16 //freopen ("G.in", "r", stdin);
17
18 int n;
19 while (scanf ("%d", &n) == 1)
20 {
21 memset (dp, 0, sizeof (dp));
22 dp[1] = 1;
23 for (int i=2; i<=n; ++i)
24 {
25 dp[i] = dp[i-1];
26 if (i > 3)
27 {
28 dp[i] += dp[i-3];
29 }
30 }
31
32 long long ans = dp[n];
33 if (n > 2)
34 {
35 for (int i=1; i<=n-2; ++i) ans += dp[i];
36 }
37 printf ("%I64d\n", ans);
38 }
39
40 return 0;
41 }