/*

     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

 */

 #include <cstdio>

 #include <algorithm>

 #include <cmath>

 #include <cstring>

 using namespace std;

 const int MAXN = 1e4 + ;

 const int INF = 0x3f3f3f3f;

 int dp[];

 int main(void)        //URAL 1260 Nudnik Photographer

 {

     //freopen ("G.in", "r", stdin);

     int n;

     while (scanf ("%d", &n) == )

     {

         memset (dp, , sizeof (dp));

         dp[] = ;

         for (int i=; i<=n; ++i)

         {

             dp[i] = dp[i-];

             if (i > )

             {

                 dp[i] += dp[i-];

             }

         }

         long long ans = dp[n];

         if (n > )

         {

             for (int i=; i<=n-; ++i)    ans += dp[i];

         }

         printf ("%I64d\n", ans);

     }

     return ;

 }