#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm> 
#include<string>
#include<cstring>
using namespace std;
int main()
{
    int n;
    while (cin >> n) {
        int arr[1000];
        arr[0] = 1, arr[1] = 2;
        for (int i = 2; i < n; i++) {
            arr[i] = arr[i - 1] + arr[i - 2];
        }
        cout << arr[n - 1] << endl;
    }

    return 0;
}