#include <iostream>
using namespace std;
long long memo[50][2] = {0};

long long sgrk(int n)
{
    if(n < 0) return 0;
    if(n < 2) return 1;
    if(memo[n-2][0] == 0){
        memo[n-2][1] = sgrk(n-2);
        memo[n-2][0] = 1;
    }
    if(memo[n-1][0] == 0){
        memo[n-1][1] = sgrk(n-1);
        memo[n-1][0] = 1;
    }
    return memo[n-2][1] + memo[n-1][1];
}

int main()
{
    int n;
    cin >> n;
    cout << sgrk(n) << endl;
    return 0;
}