#include <cstdio>
#include <cstring>
 
#define MAX 1000
 
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()
{
    freopen("nunta.in", "r", stdin);
    int n; scanf("%d", &n); fclose(stdin);
    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]);
    }
    freopen("nunta.out", "w", stdout);
    for(int i = v[(n - 1) % 3][0]; i; i--)
        printf("%d", v[(n - 1) % 3][i]);
    fclose(stdout);
    return 0;
}