#include <iostream>
using namespace std;

int func(int n)
{
    if(n == 0)
        return 0;
    else if(n == 1)
        return 1;
    else if(n == 2)
        return 2;
    else 
        return func(n-1) + func(n-2);
}

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