#include <fstream>
#include <cstring>

#define MAX 40000

using namespace std;

int v[3][MAX];

void add(int A[], int B[])
{
      int i, t = 0;
      for (i=1; i<=A[0] || i<=B[0] || t; i++, t/=10)
              A[i] = (t += A[i] + B[i]) % 10;
      A[0] = i - 1;
}

int main()
{
    ifstream in("nunta.in");
    int n; in>>n; in.close();
    int first, second, third;
    v[2][0] = v[2][1] = v[0][0] = v[0][1] = 1;
    for(int i = 1; i < n; i++)
    {
        first = i % 3; second = (i + 1) % 3; third = (i + 2) % 3;
        memset(v[first], 0, MAX * sizeof(int));
        add(v[first], v[second]);
        add(v[first], v[third]);
    }
    ofstream out("nunta.out");
    for(int i = v[n % 3][0]; i; i--)
        out<<v[(n - 1) % 3][i];
    out.close();
    return 0;
}